Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jallcom.2023.171624

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Part of collection (book)  

DOI： https://doi.org/10.1007/978-981-99-5235-9_13

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1126/sciadv.adi1744

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1361-648X/acce13

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acsaelm.3c00586

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d2tc05118d

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.202215286

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d2tc03914a

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7566/JPSJ.91.091001

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society ({APS})  

DOI： 10.1103/PhysRevMaterials.6.044412

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Language：English   Publishing type：Research paper (scientific journal)  

We have measured and analyzed the thermopower of single-crystal samples of the Mott insulator Ca2RuO4 in high pressure up to 0.9 GPa. We find that the thermopower rapidly changes at a metal-insulator transition temperature, which is explained in terms of a percolation theory. In contrast, the thermopower in the insulator phase slightly decreases with increasing pressure well below the transition temperature, and is associated with thermodynamic quantities through the Kelvin formula. The pressure dependence is compared with the current-density dependence, and a possible origin for the current-enhanced thermopower is proposed.

DOI： 10.7566/JPSJ.91.033703

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d1tc03897d

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7566/jpsj.90.114706

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/2515-7655/ac2357

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.90.063601

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0051283

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10853-021-05849-7

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1107/S2052520621000238

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.oceram.2021.100080

Scopus

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Pseudo-Ruddlesden-Popper-type Li2SrNb2O7 (LSNO), which belongs to a layered perovskite-type family, exhibits a first-order ferroelectric phase transition at 217 K. Our first-principles calculations and dielectric measurements show that Ca-substitution for Sr in LSNO enhances the rotation of NbO6 octahedra and Nb5+ displacements to induce a robustly stabilized ferroelectric P2(1)cn phase. The present study has demonstrated the two coexisting mechanisms in the ferroelectric phase transition of LSNO: the second-order Jahn-Teller effect and the rotational-distortion driven hybrid-improper ferroelectricity. The origin of unique ferroelectric phase transition of LSNO has been clarified to be softening of the zone-boundary Y-2(-) mode. The present study provides a new insight into designing ferroelectricity in layered perovskite-type oxides with the second-order Jahn-Teller effect and the rotations of octahedra.

DOI： 10.1021/acs.chemmater.0c04032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

DOI： 10.1088/1361-648x/abb866

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Other Link： https://iopscience.iop.org/article/10.1088/1361-648X/abb866/pdf

Language：English   Publishing type：Research paper (scientific journal)  

The nanostructure of relaxor ferroelectric materials has been a central focus for investigating the microscopic origin of their intriguing physical properties. While it is believed that relaxor ferroelectricity is governed by polar nanostructures, such as polar nanoregions or nanodomains, recent studies have indicated the importance of additional mechanisms, such as the competition of ferroelectric/anti-ferroelectric order and the formation of hierarchical nanodomains. This calls for further investigation on the nanostructure. Here, we used conventional, in situ, and atomic-scale electron microscopy to study prototypic relaxor ferroelectrics, Pb(Mg Nb )O (PMN) and Pb(Mg Nb )O –PbTiO (PMN-PT). We found that a lamellar-like nanostructure was present in pure PMN, which had been overlooked in past studies and did not have a strong correlation with the polar nanostructure and the chemically ordered region. Unlike the lamellar-like nanodomains in PMN-PT, the lamellar-like nanostructure in PMN was not coupled with Pb-ion displacement and was not reoriented by the presence of an electric field. The results suggested that the formation of a lamellar-like structure occurs prior to the formation of larger-scale polar order in relaxor ferroelectrics. 1/3 2/3 3 1/3 2/3 3 3

DOI： 10.1007/s10853-020-05417-5

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz  

We propose a novel and accurate method of estimating the firing temperature of ancient ceramics using terahertz (THz) wave technology. The method is based on the firing temperature dependence of the THz-wave characteristics of ceramics. Using this method, the firing temperature of an ancient Arita porcelain shard was estimated at 1240 °C, which is within the firing temperature range estimated from other methods but is more precise.

DOI： 10.1109/IRMMW-THz46771.2020.9370497

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Physical Review Materials  

Dielectric and elastic properties of aluminate-sodalite-type oxides, (Ca1-xSrx)8[AlO2]12(MoO4)2 with x=1/16 and 1/4, are investigated in the present study. A well-defined improper ferroelectric phase transition is demonstrated in the composition of x=1/16 by the onset of spontaneous strain and sharp anomalies in the dielectric and elastic responses around 600 K. As the Sr concentration increases to x=1/4, strong frequency dispersion appears in the dielectric and elastic responses, indicating that the system changes into a short-range ordered state. The dielectric and elastic anomalies are found to follow a single Vogel-Fulcher equation over a wide frequency range from 10-1 to 106Hz. The present results suggest an improper relaxor state at the composition of x=1/4, in which polar nanoregions form under spatially heterogeneous strain due to differences in the local coordination environments around Ca and Sr.

DOI： 10.1103/PhysRevMaterials.4.104413

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Unusual effects of post annealing on optical and dielectric properties of (Nb0.5In0.5)(0.01)Ti0.99O2(NITO-1.0%) are reported in the present study. The post-annealing performed under embedding in Al(2)O(3)powder changes the color of a NITO-1.0% single crystal from black to yellow. Furthermore, the apparent increase in the relative permittivity due to the Maxwell-Wagner-Sillars effect, on the order of 10(4), observed in the as-synthesized NITO-1.0% completely disappears after the post-annealing to reveal an intrinsic enhancement of dielectric response due to the co-doping of Nb and In. The relative permittivity of the post-annealed NITO-1.0% uniformly increases by approximately 120 from the original value of pure-TiO(2)over a wide temperature range from 4.2 K to room temperature. A temperature dependence of permittivity in the post-annealed NITO-1.0% shows behavior that is qualitatively identical to that of pure TiO2, indicating that the co-doping gives rise to an additional dielectric response in TiO2, probably through creation of defect complexes with large polarizability. The polarizability of the defect complex is estimated to be two hundred times greater than that of Ti4+, giving a new insight for the design of novel dielectric materials with large permittivity by means of complex defect engineering.

DOI： 10.1039/d0tc03539d

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Applied Physics  

Improper ferroelectric Ca8-xSrx[Al12O24](MoO4)2 (x = 0-2) multilayer capacitors (MLCs) were fabricated to study their dielectric and ferroelectric properties for their potential practical applications and reversible switching of electric polarization by an electric field. The substitution of Sr for Ca caused a structural change from polar orthorhombic to non-polar cubic phases at 297 K and decreased the ferroelectric phase transition temperature (Tc). Spontaneous polarization up to ∼0.6 μC/cm2 was performed at 297 K in Ca7.5Sr0.5[Al12O24](MoO4)2 and Ca7Sr[Al12O24](MoO4)2 MLCs by poling with an electric field of 10 MV/m. Furthermore, ferroelectric hysteresis loops from the electric polarization switching were successfully demonstrated in Ca8[Al12O24](MoO4)2 MLCs above 469 K by the application of a high electric field over 50 MV/m, and remnant electric polarization of ∼0.59 μC/cm2 was obtained at 573 K. The results introduce a new avenue for possible applications and new functionalities of improper ferroelectrics with an MLC structure.

DOI： 10.1063/5.0016533

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have measured and analyzed the nonlinear conduction of the Mott insulator Ca2RuO4 with square wave and square-pulse currents around room temperature with an infrared camera as a contactless thermometer. By combining the thermal diffusivity measurements, we have found that the temperature increase due to self heating is explained by the conduction of the Joule heat through the sample to the heat bath. We further find a time scale of the nonlinear conduction to be 20 ms, which is consistent with thermal relaxation time of the sample. We propose that a steady dissipation of external energy flow characterizes the non-equilibrium steady state of Ca2RuO4, rather than a steady current flow.

DOI： 10.7566/JPSJ.89.093707

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本物理学会  

ファイル公開：2021-09-15

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

© 2020 American Physical Society. When light is absorbed in solids, electrical conductivity is usually enhanced through generation of photodoped conductive carriers, known as photoconduction. Here we show UV-light absorption restrains photoconduction, but markedly enhances dielectric permittivity in a ceramic sample of LaAlO3 with defects introduced deliberately by reduction synthesis. Using systematic dielectric measurements under photoirradiation combined with computational studies for defect formation energies, we explain this unconventional photoinduced phenomenon in terms of photoexcited dipoles: The photoexcited electrons are trapped in in-gap states introduced by oxygen vacancies whereas photoexcited holes are localized in a valence-band maximum. Thus the created electron-hole pair acts as an electric dipole to enhance the dielectric permittivity. This unprecedented photoelectric effect does not only provide an alternative functionality for dielectric materials, but also paves the way for next-generation photoelectronic devices.

DOI： 10.1103/PhysRevB.101.184114

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We report that the volume of an orbital-ordered Mott insulator Ca2RuO4 is purely changed by an electrical current at constant temperature and pressure. The observed giant electromechanical response is an intrinsic non-equilibrium property in currents, not from an extrinsic self-heating effect, as is clearly demonstrated by combined transport and synchrotron radiation X-ray diffraction experiments. The underlying mechanism is ascribed to a suppression of orbital order by currents, significantly differing from conventional piezoelectric or electrostrictive effect in dielectric materials. Our results imply a novel non-equilibrium equation of state, in which an equilibrium quantity is described by a non-equilibrium variable, and thus provide fundamental data for investigating the evolving field of non-equilibrium thermodynamics.

DOI： 10.7566/JPSJ.89.044710

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The excitonic insulator candidate Ta2NiSe5 has been examined by means of the response to a pulse electric field. We observed linear current-voltage relationship at 200V/cm, indicating the robustness of the exciton binding state in Ta2NiSe5.

DOI： 10.7566/JPSJ.89.045001

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Copyright © 2020 American Chemical Society. Pseudo Ruddlesden-Popper-type Li2SrNb2O7 undergoes a phase transition between paraelectric and weak ferroelectric phases at Tc (=217 K), whereas Ta-counterpart Li2SrTa2O7 stays paraelectric though its room temperature structure is identical to that of Li2SrNb2O7. In the present study, the ferroelectric phase transition of Li2Sr(Nb1-xTax)2O7 is investigated as a function of Ta-concentration x. As the Ta-concentration x increases, Tc is found to decrease monotonously, leading to the disappearance of the ferroelectricity at x = 0.4. This phase-transition suppression with increasing x in Li2Sr(Nb1-xTax)2O7 is supported by first-principles calculations, showing that the soft mode in Li2SrNb2O7 or the increase of x in Li2Sr(Nb1-xTax)2O7 enhances their bonding states. In the composition of x = 0.4, dielectric permittivity gradually increases on cooling to become independent of temperature around 0 K, indicating an incipient ferroelectricity of the system. Empirical analyses suggest existence of a quantum paraelectric state in a composition range of 0.3 < x < 0.4. The present study provides a novel playground to investigate a quantum para/ferroelectricity in layered-perovskite-type compounds.

DOI： 10.1021/acs.chemmater.9b04022

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electrical Engineers of Japan  

DOI： 10.1541/ieejjournal.140.28

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Copyright © 2019 American Chemical Society. Structural phase transitions of calcium strontium sulfoaluminate series, (Ca1-xSrx)8[AlO2]12(SO4)2 ((CS)AS-x) with x = 0.80-1.00, are systematically investigated by powder X-ray diffraction, dielectric measurements, and pyroelectric measurements, to clarify a phase diagram of (CS)AS-x (x = 0.80-1.00). A pure strontium sulfoaluminate, (CS)AS-1.00, is found to undergo three phase transitions, which take place successively on cooling from a prototypical cubic phase with the symmetry of Im3 m. Though the room-temperature phase of (CS)AS-1.00 was previously reported to be of polar Pcc2, the pyroelectric measurements clarified a nonpolar character of the crystal symmetry. The dielectric measurements suggest a possibility of an antiferroelectric ground state of (CS)AS-x in the Sr-rich compositions. As x decreases, the ground state changes to a short-range-ordered state, implying a unique phase transition from the antiferroelectric state to the antiferroelectric-relaxor state. The present study provides an intriguing playground for designing new ferro/antiferroelectric materials.

DOI： 10.1021/acs.inorgchem.9b02495

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本物理学会  

We have measured the dielectric constant and thermopower of single crystal samples of the excitonic insulator candidate Ta2NiSe5. The dielectric constant below 50 K shows relaxor-like relaxation, implying the existence of randomly distributed electric dipoles. We have evaluated the concentration of the dipoles to be 10^19 cm^−3 at 30 K, which gives a rough estimate of the exciton concentration in this compound. A large thermopower of 600 µV/K at 100 K suddenly drops toward zero down to 50 K, and this zero thermopower evidences the neutral particles flow against the applied temperature gradient. We have semi-quantitatively explained the above two anomalies in terms of spontaneously generated excitons at low temperatures where thermally excited holes are quenched.ファイル公開：2020/11/15

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

© 2019 American Chemical Society. Li2SrNb2O7 (LSNO) crystallizes in a structure closely related to n = 2 Ruddlesden-Popper-type compounds, which are generally formed by intergrowth of two-dimensional perovskite-type blocks and rocksalt-type layers. The present study demonstrates the coexistence of spontaneous polarization and an anti-ferroelectric-like nonlinear response in LSNO at 80 K, suggesting weak ferroelectricity below the phase transition temperature of 217 K. A combination of first-principles calculations and single-crystal X-ray diffractions clarifies a polar P21cn structure for the ground state of LSNO, where an in-plane antiferroelectric displacement and an out-of-plane polar shift simultaneously take place. The present study offers a new perspective to design ferroelectric and antiferroelectric materials with Ruddlesden-Popper-type compounds.

DOI： 10.1021/acs.chemmater.9b02373

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society of Pediatric Surgeons  

<p><i>Purpose</i>: To examine the effectiveness of taping treatment for infantile umbilical hernia, a retrospective questionnaire survey was carried out in the pediatric surgery institutes in the Kyushu Pediatric Surgery Study Group.</p><p><i>Methods</i>: Infants with umbilical hernia registered from January 2013 to December 2015 were included in this study. Their therapeutic results were assessed at the end of June 2016.</p><p><i>Results</i>: Replies were obtained from 24 institutes. Cure was judged on the basis of the closure of the hernia orifice. The number of infants who underwent the taping treatment was 1,320. Cure was achieved in 908 infants, whereas no cure was found in 158 infants; 48 infants dropped out owing to skin disorders and results were not known in 206. Among the 333 infants in whom monitoring without treatment was performed, spontaneous cure was seen in 146 infants and no cure in 111 infants; results were not known in 76. The cure rate of taping treatment was significantly higher than that of monitoring without treatment (85.2% vs. 56.8%, <i>p</i><0.05, χ² test). Furthermore, the duration until cure was less than 4 months in about 80% of the infants with taping treatment, whereas the duration in many infants monitored without treatment was more than 1 year.</p><p><i>Conclusions</i>: The taping treatment for infantile umbilical hernia shortened the duration until cure, but the cure rate of this treatment did not exceed the 90% spontaneous cure rate of the untreated patients at 2 years of age as described in conventional textbooks. However, the spontaneous cure rate found by our questionnaire survey was unexpectedly low. Therefore, the spontaneous cure rate of infantile umbilical hernia should be further investigated by prospective studies.</p>

DOI： 10.11164/jjsps.55.5_920

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

© 2019 Author(s). We report the electrical conductivity and the Seebeck coefficient of a SrTiO 3 single crystal under 405-nm laser illumination from 10 to 30 K. We find that the photoconductivity exponentially increases with decreasing temperature, suggesting a gradual metal-insulator transition. Assuming the carrier mobility reported in the preceding studies, we have evaluated the carrier concentration to be 8 × 10 9 cm - 3 at maximum, which corresponds to 10 - 7 ppm impurities in the case of chemical doping. Such ultralow doping is realized only when the energy of the incident light is slightly lower than the bandgap. In this situation, the incident light penetrates the whole sample with a small probability of electron-hole creation. We find that the observed photo-Seebeck coefficient seriously disagrees with the calculated values from the carrier concentration. In order to remedy this discrepancy, we have proposed a phenomenological model in which the quantum paraelectric behavior of SrTiO3 screens the thermoelectric voltage.

DOI： 10.1063/1.5106384

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

© 2019 American Chemical Society. Molecular ferroelectric crystals have attracted growing interest as potential alternatives to conventional lead-based ceramic ferroelectrics. We have recently discovered that a class of compounds known as plastic crystals can show multiaxial ferroelectricity, which allows ferroelectric performance even in polycrystalline forms. Here, we report new plastic/ferroelectric ionic molecular crystals that exhibit remarkably small coercive electric fields at room temperature. The easily switchable ferroelectric polarization enables low-voltage switching operations and high-frequency performance. Such ferroelectric crystals can be readily processed into bulk polycrystalline forms with desired shapes that are characterized by unprecedentedly high pyroelectric figures of merit and large piezoelectricity. These multifunctional molecular crystals represent highly attractive prospects for device elements with a diverse range of applications, which will significantly boost the development of molecular ferroelectric crystals.

DOI： 10.1021/jacs.9b03369

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2019 American Physical Society. The high-pressure structural properties of bismuth oxide Bi2SiO5 have been investigated up to 29 GPa using in situ powder synchrotron x-ray diffraction (XRD) and up to 50 GPa with density functional theory (DFT) calculations. We found a compressibility anomaly at about 20 GPa that is observed both in our XRD and DFT results. The rotation of the corner-connected SiO4 tetrahedra produces a straightening of the silicate chains, yielding a lower compressibility above 20 GPa for the structure with straight chains. We analyzed the stereochemical activity of the Bi3+ lone electron pair, which is found to decrease with increasing pressure, but it can still be identified in the calculated electron density difference maps at 50 GPa.

DOI： 10.1103/PhysRevB.99.064116

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Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2019, © 2019 Taylor & Francis Group, LLC. High-energy X-ray diffraction study was performed on lead titanate (PbTiO3). Short-range order structure was revealed using atomic pair-distribution function (PDF) method. In the high-temperature cubic phase, there is a large deviation between local and average structure. Especially, Pb atoms deviated from the cubic lattice framework, but establish Pb-O-Pb random network.

DOI： 10.1080/00150193.2019.1569986

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

©2019 The Physical Society of Japan Structural phase transitions of strontium-substituted calcium sulfoaluminates, (Ca1−xSrx)8[AlO2]12(SO4)2 [(CS)AS-x], are systematically investigated by powder X-ray diffraction (PXRD) and dielectric measurements. In a pure calcium sulfoaluminate (CS)AS-0.0, an unreported phase transition and dielectric anomaly are found in the low-temperature region below the ferroelectric phase-transition temperature. The XRD pattern recorded as a function of Sr substitution and temperature clearly resolves Tc suppression with Sr content x from a structural change perspective. Although no macroscopic change in the crystal structure is observed for (CS)AS-0.4, the broad dielectric peak with frequency dispersion remains for this composition, indicating the fragmentation of polar ordering. Furthermore, (CS)AS-0.4 shows a specific heat anomaly along with the broad dielectric peak, suggesting a relaxor-like short-range ordered state of the system.

DOI： 10.7566/JPSJ.88.034718

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

© 2019 American Chemical Society. Transparent conducting oxide (TCO) is a promising material system for transparent electrodes, which is one of the most essential elements in current electronic and energy devices. In particular, In-based TCOs such as Sn:In2O3 (ITO) and In-Ga-Zn-O (IGZO) have shown large optical band gap and high electrical conductivity, sufficient for the applications. However, In is an expensive element, which hampers its facile industrial application. Moreover, In-based TCOs show an abrupt decrease in conductivity when their thickness decreases below ∼100 nm, possibly due to inhomogeneity within the thin films. Here, we introduce an amorphous Ca-Al-O (CAO) thin film as a promising candidate for the In-free TCOs. The amorphous CAO thin film has very low resistivity (∼10-5 ω cm) at room temperature, as well as high transparency in the visible region of the light spectrum (>80%). The isotropic Ca s-orbital in the conduction band is found to be responsible for the superior performance of CAO as a TCO. Owing to the exceptional structural homogeneity of the CAO thin film, thickness-independent transport characteristics are observed, maintaining its TCO performance down to 10 nm of thickness.

DOI： 10.1021/acs.chemmater.9b02399

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

©2019 The Physical Society of Japan We have measured the dielectric constant and thermopower of single crystal samples of the excitonic insulator candidate Ta2NiSe5. The dielectric constant below 50 K shows relaxor-like relaxation, implying the existence of randomly distributed electric dipoles. We have evaluated the concentration of the dipoles to be 1019 cm−3 at 30 K, which gives a rough estimate of the exciton concentration in this compound. A large thermopower of 600 µV=K at 100 K suddenly drops toward zero down to 50 K, and this zero thermopower evidences the neutral particles flow against the applied temperature gradient. We have semi-quantitatively explained the above two anomalies in terms of spontaneously generated excitons at low temperatures where thermally excited holes are quenched.

DOI： 10.7566/JPSJ.88.113706

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

<p>Our group has recently found improper ferroelectric materials in aluminate-sodalite-type compounds that belong to a zeolite-family. The aluminate-sodalite-type compounds are mainly composed of eco-friendly elements, which are ubiquitous in the earth's crust. A conventional strategy for the development of ferroelectric materials is based on perovskite-type compounds, leading to many practical applications for device elements such as capacitors and frequency filters. Aluminate-sodalite-type ferroelectrics, on the other hand, show excellent performance for pyroelectric energy harvesting, which exceeds that of lead-based perovskite-type compounds, indicating the potential of non-perovskite-type ferroelectrics for functional materials. Here we give an overview of the improper ferroelectricity in aluminate-sodalite-type compounds and discuss their performance for pyroelectric energy harvesting in connection with their improper ferroelectricity.</p>

DOI： 10.11470/oubutsu.88.10_668

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.1.0_2549

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.1.0_2550

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.1.0_2551

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

© 2018 Author(s). Systematic tuning of photo-induced enhancement of the dielectric permittivity (i.e., the photo-dielectric effect) in Ba(Al1-xZnx)2O4-δ (BAZ-x) has been demonstrated by changing Zn concentration x and intensity of the incident light. The relative change of the dielectric permittivity (ϵ′), defined as Δϵ′photo/ϵ′dark, increases linearly with an increase in the Zn concentration (x), finally reaching approximately 30% at 1 MHz. The dependence of Δϵ′photo/ϵ′dark on the intensity of the incident light shows a two-step growth as the irradiation light intensity increases, suggesting the existence of multiple photo-induced processes influencing the photo-dielectric effect of BAZ-x. The results of the present study not only give a clue to the mechanism of the photo-dielectric effect but also aid in the development of innovative photo-tunable functional devices.

DOI： 10.1063/1.5036982

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CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2018 American Physical Society. We have measured the reflectivity spectra of the barium iridate 9RBaIrO3, the crystal structure of which consists of characteristic Ir3O12 trimers. In the high-temperature phase above the transition temperature Tc≃180 K, we find that the optical conductivity involves two temperature-dependent optical transitions with an ill-defined Drude response. These features are reminiscent of the optical spectra in the organic dimer Mott insulators, implying a possible emergence of an unusual electronic state named trimer Mott insulator in BaIrO3, where the carrier is localized on the trimer owing to the strong Coulomb repulsion. Along with a pronounced splitting of the phonon peak observed below Tc, which is a hallmark of charge disproportionation, we discuss a possible phase transition from the trimer Mott insulator to a charge-ordered insulating phase in BaIrO3.

DOI： 10.1103/PhysRevB.98.205131

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. We have prepared a set of polycrystalline samples of La0.8Sr0.2Co1−xAlxO3 (0 ≤ x ≤ 0.2), and have measured the magnetization as functions of temperature and magnetic field. We find that the average spin number per Co ion (SCo) evaluated from the room-temperature susceptibility is around 1.2–1.3 and independent of x. However, we further find that SCo evaluated from the saturation magnetization at 2 K is around 0.3–0.7, and decreases dramatically with x. This naturally indicates that a significant fraction of the Co3+ ions experience a spin-state crossover from the intermediate-to low-spin state with decreasing temperature in the Al-substituted samples. This spin-state crossover also explains the resistivity and the thermopower consistently. In particular, we find that the thermopower is anomalously enhanced by the Al substitution, which can be consistently explained in terms of an extended Heikes formula.

DOI： 10.3390/cryst8110411

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Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2018 American Physical Society. The lattice dynamics of Bi2SiO5 has been studied by x-ray thermal diffuse scattering (TDS), inelastic x-ray scattering (IXS), and density functional theory calculations across the ferroelectric transition at TC=663 K. Rodlike diffuse features are observed along the [100] direction, perpendicular to the direction of the quasi-one-dimensional silicate chains. IXS measurements of the phonon dispersion along the [100] Γ-Y direction related these diffuse features to coupled unstable transverse optic and acoustic branches. A strong temperature-dependent TDS signal was also observed at the Brillouin zone edges, at the Y and S points, indicating a competition between ferroelectric and antiferroelectric distortions. We observed with IXS a substantial but finite phonon softening at the Y point and a minor softening at the S point, that are associated with the displacement of oxygen atoms. The good agreement between the experiment and the theoretical TDS and IXS allows us to provide a quantitative overview of the various lattice dynamical instabilities occurring at TC. The direct evidence for competing ferroelectric and antiferroelectric orders opens the way towards tuning the properties of Bi2SiO5 by application of pressure or electrical field.

DOI： 10.1103/PhysRevB.98.134102

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

© 2018 IOP Publishing Ltd. We have investigated the dilute magnetic impurity effect on the magnetic properties of a quantum spin liquid candidate Ba3ZnRu2O9 and a spin gapped compound Ba3CaRu2O9. The magnetic ground state of each compound stands against 2% substitution of magnetic impurities for Zn or Ca. We have found that the magnetic response of these impurities, which behave as paramagnetic spins, depends on the host materials and the difference of the two manifests itself in the Weiss temperature, which can hardly be explained by the dilute magnetic impurities alone in the case of Ba3ZnRu2O9. We consider a contribution from the Ru5+ ions which would appear only in the substituted Ba3ZnRu2O9 and discuss a possible physical meaning of the observed Weiss temperature.

DOI： 10.1088/1361-648X/aad5ac

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

© 2018 American Physical Society. This paper focuses on effects of isovalent La substitution on the crystal structure and dielectric properties of ferroelectric Bi2SiO5. Polycrystalline samples of (Bi1-xLax)2SiO5 are synthesized by crystallization of Bi-Si-O and Bi-La-Si-O glasses with a composition range of 0≤x≤0.1. The crystal structure changes from monoclinic to tetragonal with increasing La-substitution rate x at room temperature. This structural variation stems from the change in orientation of SiO4 tetrahedra that form one-dimensional chains when they are in the ordered configuration, thus suggesting that lone-pair electrons play an important role in sustaining one-dimensional chains of SiO4 tetrahedra. Synchronizing with the disordering of SiO4 chains, ferroelectric phase transition temperature of (Bi1-xLax)2SiO5 sharply decreases as x increases, and ferroelectricity finally vanishes at around x=0.03. The present results demonstrate that lone-pair electrons of Bi play an important role in the ferroelectricity of Bi2SiO5 through propping the ordered structure of one-dimensional SiO4 chains with stereochemical activity. Furthermore, an additional phase transition has been first discovered in the low-temperature region of (Bi1-xLax)2SiO5 with x≤0.01, where the ordered one-dimensional SiO4 chains remain.

DOI： 10.1103/PhysRevMaterials.2.045603

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

© 2018 The Physical Society of Japan. We have successfully synthesized a set of polycrystalline samples of CaPd3-xCuxO4 from x = 0 to 2.4, and measured the resistivity, thermopower and susceptibility down to 4K. We find that the solid solution between Pd and Cu systematically evolves the electronic ground states from a conventional band insulator to a correlated Mott insulator. In particular, CaPd0.6Cu2.4O4 shows a magnetic phase transition at 20 K. A partial substitution of La and Y for Ca supplies electrons to CaPd0.6Cu2.4O4, and decreases the room-temperature resistivity smaller than 10ωcm.

DOI： 10.7566/JPSJ.87.104603

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CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.73.2.0_897

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.73.1.0_2199

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.73.2.0_2130

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

© 2017 Author(s). Photo-induced persistent enhancement of dielectric permittivity has been demonstrated in Ba(Al0.97Zn0.03)2O4-δ (BAZ) with a stuffed-Tridymite-Type structure under photo-irradiation with an energy of 3.4 eV (365 nm). The dielectric permittivity is enhanced by more than 20% and shows a weak frequency dependency. The dielectric loss (tanδ) shows only a slight increment for frequencies up to 1 MHz, indicating that the incremental change in dielectric permittivity of BAZ is not caused by photoconduction. This enhancement persists on termination of photo-irradiation. The results of this study suggest that the origin of the enhancement of dielectric permittivity is related to the dielectric response of the photo-excited dipole moments, which are composed of photo-excited electrons trapped in in-gap states and photo-excited holes generated in the valence band maximum. These findings shed light on the development of devices that can control dielectric properties by photo-irradiation.

DOI： 10.1063/1.5001369

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

© 2017 The Author(s). The development of dielectric materials with colossal permittivity is important for the miniaturization of electronic devices and fabrication of high-density energy-storage devices. The electron-pinned defect-dipoles has been recently proposed to boost the permittivity of (Nb + In) co-doped TiO2 to 105. However, the follow-up studies suggest an extrinsic contribution to the colossal permittivity from thermally excited carriers. Herein, we demonstrate a marked enhancement in the permittivity of (Nb + In) co-doped TiO2 single crystals at sufficiently low temperatures such that the thermally excited carriers are frozen out and exert no influence on the dielectric response. The results indicate that the permittivity attains quadruple of that for pure TiO2. This finding suggests that the electron-pinned defect-dipoles add an extra dielectric response to that of the TiO2 host matrix. The results offer a novel approach for the development of functional dielectric materials with large permittivity by engineering complex defects into bulk materials.

DOI： 10.1038/s41598-017-05651-z

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

©2017 The Physical Society of Japan. We have measured the resistivity, the thermopower, and the specific heat of the weak ferromagnetic oxide CaRu0.8Sc0.2O3 in external magnetic fields up to 140 kOe below 80 K. We have observed that the thermopower Q is significantly suppressed by magnetic fields at around the ferromagnetic transition temperature of 30 K, and have further found that the magneto-thermopower QðH; TÞ ¼ QðH; TÞ Qð0; TÞ is roughly proportional to the magneto-entropy SðH; TÞ ¼ SðH; TÞ Sð0; TÞ. We discuss this relationship between the two quantities in terms of the Kelvin formula, and find that the observed ΔQ is quantitatively consistent with the values expected from the Kelvin formula, a possible physical meaning of which is discussed.

DOI： 10.7566/JPSJ.86.104707

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CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

© 2017 The Japan Society of Applied Physics. Dielectric measurements are performed on (Nb1/2In1/2)0.02Ti0.98O2 (NITO-2.0) single crystals grown by a floating zone method to address the nature of the colossal permittivity recently reported in (Nb + In) co-doped TiO2 ceramics. The colossal permittivity of the order of 105, which is also observed in the NITO-2.0 single crystals, disappears in the lowest temperature region, indicating an extrinsic contribution from thermally excited carriers to the colossal permittivity. Even at low temperatures where the thermally excited carriers are expected to be frozen out, a high permittivity of the order of 103 remains. This finding suggests that an intrinsic contribution from electron-pinned defect dipoles boosts the dielectric permittivity of TiO2.

DOI： 10.7567/JJAP.56.10PC02

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

©2017 The Physical Society of Japan. We have prepared polycrystalline samples of Gd2Ru2O7, and have measured the dielectric constant, magnetization and magnetostriction in external fields from 0 to 7 T below 15 K. We find that the dielectric constant of Gd2Ru2O7 significantly changes with external fields, and reveal a finite magnetoelectric coupling in this oxide. Using a simple model in which the spins on the Gd ions feel an internal magnetic field of 7 T from the Ru clusters, we have explained magnetization and magnetoelectric effects qualitatively.

DOI： 10.7566/JPSJ.86.084708

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CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

© 2017 The Japan Society of Applied Physics. An inductor is composed of a coil, and its design has seen little progress since its inception more than one hundred years ago. We propose a novel method of inducing inductance in a non-ohmic conductor. In this paper, we report a giant inductance of 42H in Ca2RuO4 in the low frequency region at room temperature, as an example. The quality (Q) factor, defined as the ratio between the imaginary and real parts of impedance, approaches infinity in the static limit. Our inductor, therefore, displays ideal characteristics such as a large inductance and high Q factor, and it may be a prime candidate for next-generation inductors.

DOI： 10.7567/APEX.10.081801

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

© 2017 Taylor & Francis Group, LLC. We performed local structure analyses of relaxor ferroelectric of lead magnesium niobate (PMN) by combining an extended X-ray absorption fine structure (EXAFS) and atomic pair-distribution function (PDF) methods. EXAFS study revealed that Pb atoms of PMN are disordered largely compared with those of PbTiO3, though the local environment of the Nb atoms is not significantly different from that for NaNbO3 and AgNbO3. The PDF analysis also revealed the short-range order structure of Pb, which is deviated from the perovskite framework.

DOI： 10.1080/00150193.2017.1350050

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

© 2017 Taylor & Francis Group, LLC. Sodium metavanadate has pyroxene-type one dimensional VO4-tetrahedral chains, which is analogous to the SiO4-chains in Bi2SiO5. Although it is known to undergo ferroelectric phase transition, its mechanism has not been clarified. This paper shows the spectroscopic results of simultaneous measurement of Raman/Brillouin scattering by utilizing ultra-narrowband holographic notch filters. The spectroscopic anomalies accompanying to the phase transition were observed for the first time in both Raman and Brillouin regimes.

DOI： 10.1080/00150193.2017.1355146

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

© 2017 IOP Publishing Ltd. We have measured the infrared reflectivity of single-crystalline samples of LaCo1-xRhxO3 (x = 0, 0.05 and 0.10) from 10 to 300 K from 0.05 to 0.15 eV. We find that the optical phonons of the Co-O stretching mode depend on temperature and the Rh content. Analysis with three Lorentz oscillators reveals that the spin state of Co3+ in LaCo1-xRhxO3 can be understood in terms of a solid solution of low-spin- and high-spin-state Co3+ ions, and the substituted Rh ion retains some fraction of the high-spin Co3+ ions down to low temperature.

DOI： 10.1088/1361-648X/aa6ebc

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

DOI： 10.1016/j.cap.2017.03.013

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/resp.12936

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim An improper ferroelectric is a certain type of ferroelectrics whose primary order parameter is not polarization but another physical quantity such as magnetization. In contrast to a conventional proper ferroelectrics as represented by Pb(Zr,Ti)O3 and BaTiO3, the improper ferroelectrics has been inconceivable for practical applications thus far. Herein, we illustrate the great potential of improper ferroelectrics for efficient conversion of temperature fluctuation to electric energy, as demonstrated with (Ca0.84Sr0.16)8[AlO2]12(MoO4)2 (CSAM-16). The present study has experimentally proven that CSAM-16 achieves an excellent electrothermal coupling factor and high electric field sensitivity for pyroelectric energy conversion that approach a practical level for application to self-powered autonomous electronic devices for rapidly spreading wireless sensor networks. The present results provide a novel approach to developing innovative pyroelectric energy harvesting devices using improper ferroelectrics.

DOI： 10.1002/pssr.201700009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

© 2017 Author(s). A photo-dielectric effect (i.e., a change in dielectric permittivity due to photo-irradiation) has been demonstrated in LaAl0.99Zn0.01O3-δ. Photo-irradiation with an incident energy of 3.4 eV was found to enhance the dielectric permittivity in LaAl0.99Zn0.01O3-δ over a wide frequency range from 100 Hz to 1 MHz. The change in dielectric permittivity in the high-frequency region hardly depended on frequency and was not accompanied by an increase in dielectric loss, indicating an intrinsic photo-dielectric effect in LaAl0.99Zn0.01O3-δ that is not due to photo-conduction. The dependence of the photo-dielectric effect on incident energy suggests the existence of deep in-gap states introduced by Zn substitution. The mechanism of the photo-dielectric effect in LaAl0.99Zn0.01O3-δ relates to the dielectric response of the photo-excited electrons trapped in the deep in-gap states, which work as effective polar displacements under an applied electric field. These findings are expected to contribute to the development of photo-capacitors that enable the remote control of the dielectric response via photo-irradiation.

DOI： 10.1063/1.4979644

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

© 2017 American Physical Society. In the present study, we demonstrate ferroelectricity in stuffed aluminate sodalites (Ca1-xSrx)8[AlO2]12(WO4)2 (x≤0.2) (C1-xSxAW). Pyroelectric measurements clarify switchable spontaneous polarization in polycrystalline C1-xSxAW, whose polarization values are on the order of 10-2 μC/cm2 at room temperature. A weak anomaly in the dielectric permittivity at temperatures near the ferroelectric transition temperature suggests improper ferroelectricity of C1-xSxAW for all investigated values of x. A comprehensive study involving synchrotron x-ray powder diffraction measurements, molecular dynamics simulations, and first-principles calculations clarifies that the ferroelectric phase transition of C1-xSxAW is driven by the freezing of the fluctuations of WO4 tetrahedra in the voids of an [AlO2]1212- framework. The voltage response and electromechanical coupling factor of C1-xSxAW estimated from the present results indicate that this material exhibits excellent performance as a pyroelectric energy harvester, suggesting that aluminate sodalites exhibit great promise as a class of materials for highly efficient energy-harvesting devices.

DOI： 10.1103/PhysRevApplied.7.034012

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Scopus

Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

©2017 The Physical Society of Japan. We have discovered a novel candidate for a spin liquid state in a ruthenium oxide composed of dimers of S = 3/2 spins of Ru5+, Ba3ZnRu2O9. This compound lacks a long range order down to 37 mK, which is a temperature 5000-times lower than the magnetic interaction scale of around 200 K. Partial substitution for Zn can continuously vary the magnetic ground state from an antiferromagnetic order to a spin-gapped state through the liquid state. This indicates that the spin-liquid state emerges from a delicate balance of inter- and intra-dimer interactions, and the spin state of the dimer plays a vital role. This unique feature should realize a new type of quantum magnetism.

DOI： 10.7566/JPSJ.86.033702

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CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.72.1.0_2719

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.72.2.0_2057

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2016 The Author(s). Phonon transport is an essential property of thermoelectric materials. Although the phonon carries heat, which reduces the thermoelectric efficiency, it contributes positively to the Seebeck coefficient S through the phonon-drag effect, as typified by the high-purity semiconductors, which show fairly large S at cryogenic temperatures. Although such a large S is attractive in terms of Peltier cooling, a clear guiding principle for designing thermoelectric materials enriched by the phonon-drag effect remains to be established. Here we demonstrate that a correlated semiconductor, FeSb2, is a promising thermoelectric material featuring quasi-ballistic phonons dragging d electrons with large effective mass. By changing the sample size within the sub-millimetre order for high-purity single crystals, we succeed in substantially increasing S to as much as -27 mV K-1 at low temperatures. Our results exemplify a strategy for exploring phonon-drag-based thermoelectric materials, the performance of which can be maximized by combining heavy electrons with ballistic phonons.

DOI： 10.1038/ncomms12732

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

© 2016 IOP Publishing Ltd. We report on the optical properties of the layered Co oxides Bi2-xPbxSr2Co2O8 with x = 0 and 0.4 and discuss similarities among optical sheet conductivities of layered Co and Cu oxides. Optical sheet conductivity is defined as the product of the optical conductivity and the lattice parameter along the cross-layer direction. Although the optical conductivity spectra of both Bi2-xPbxSr2Co2O8 with x = 0 and 0.4 are similar in shape to Na0.75CoO2 and Ca3Co4O9 below 3 eV, they are much smaller in magnitude. In contrast, optical sheet conductivities are roughly identical among the four Co oxides below 3 eV, which indicates that the common CoO2 layer in these oxides has the same electronic state. In addition, we find that optical sheet conductivities are identical among the layered Cu oxides with a four-fold coordinated CuO4 plane. We suggest using optical sheet conductivity as a key concept to discuss the similarity among the layered materials.

DOI： 10.1088/0953-8984/28/32/325501

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

© 2016 American Physical Society. We investigated the structural phase transition of BaAl2O4, which has a network structure with corner-sharing AlO4 tetrahedra, via synchrotron x-ray thermal diffuse scattering measurements and first-principles calculations. BaAl2O4 shows the structural phase transition at TC=451.4 K from the P6322 parent crystal structure to the low-temperature superstructure with a cell volume of 2a×2b×c. This phase transition is unusual, in which two energetically competing phonon modes at M and K points soften simultaneously. When approaching TC from above, the K-point mode appears first. However, this K-point mode is overcome by the later-developed M-point mode. The thermal diffuse scattering intensities from both modes increase sharply at TC; therefore, both modes soften simultaneously. The first-principles calculations demonstrate that the M-point mode is electrostatically more preferable than the K-point mode and determines the eventual low-temperature structure, although these two modes are competing energetically. This competition is characteristic of BaAl2O4, which is ascribed to the structurally flexible network structure of this compound.

DOI： 10.1103/PhysRevB.93.134108

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

© 2016 by the authors; licensee MDPI, Basel, Switzerland. We have prepared polycrystalline samples of the trimer Ir oxide BaIrO3 with face-shared Ir3O12 trimers, and have investigated the origin of the phase transition at 182 K by measuring resistivity, thermopower, magnetization and synchrotron X-ray diffraction. We propose a possible electronic model and transition mechanism, starting from a localized electron picture on the basis of the Rietveld refinement. Within this model, BaIrO3 can be basically regarded as a Mott insulator, when the Ir3O12 trimer is identified to one pseudo-atom or one lattice site. The transition can be viewed as a transition from the Mott insulator phase to a kind of charge ordered insulator phase.

DOI： 10.3390/cryst6030027

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Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

© 2016 AIP Publishing LLC. Useful dielectric properties for high-temperature ceramic capacitors are demonstrated in a non-perovskite oxide, Ca(Ti0.85 Zr0.15)SiO5, which is mainly composed of one-dimensional chains of oxygen octahedra that are mutually linked by SiO4 tetrahedra. Its dielectric constant and low temperature coefficient of capacitance were found to be 43 and -102 ppm/K, respectively, over the wide temperature range of 300-780 K. The high insulating performance was also indicated by the high resistivity, exceeding 1011 Ω cm up to 523 K. The systematic dielectric measurements for Ca(Ti1-x Zrx)SiO5 as functions of the composition and temperature indicate that the suppression of the anti-ferroelectric phase transition of CaTiSiO5 by Zr4+-substitution is a key to improve the temperature-stability and the high-resistivity in Ca(Ti1-x Zrx)SiO5. The present results shed light on the development of a designing principle for ceramic capacitors for the high-temperature use.

DOI： 10.1063/1.4941803

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

© 2016 IOP Publishing Ltd. We report the optical properties of layered calcium cobaltate, Ca3Co4O9, which is regarded as a promising candidate for use as a thermoelectric material. The optical conductivity shows three broad peaks related to the inter-band transition below 4 eV, which are quite similar to those in the spectra of NaxCoO2. This similarity implies that the CoO2 layer, which is an essential unit for both Ca3Co4O9 and NaxCoO2, is dominant in the energy band structure below 4 eV. In addition, we estimate the effective carrier number per Co site and find similarity between the CoO2 layers of Ca3Co4O9 and Na0.75CoO2, which is consistent with the similarity in their Seebeck coefficients. To discuss the contribution of the rocksalt-type Ca2CoO3 layer in Ca3Co4O9, we propose the concept of optical sheet conductivity in the layered materials and estimate its value in the Ca2CoO3 layer. A comparison with the spin-polarized band calculation of the LDA + Hubbard U formalism with U = 5 eV suggests that the Ca2CoO3 layer has the inter-band transition of 2.6 eV in the spin-down band structure. Evaluation of the valences of Co 3d orbitals indicates the existence of charge transfer from the Ca2CoO3 layer to the CoO2 layer and mixing of Co3+ and Co4+ in the CoO2 layer, which may be the origin of the large thermoelectric effect.

DOI： 10.1088/0953-8984/28/8/085601

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

© 2016 The Physical Society of Japan. We have investigated both static and dynamic magnetic properties of polycrystalline CaRu1-xScxO3 system in order to clarify the role of Sc ions as a disorder for magnetic ordering. We have observed typical features of a ferromagnetic cluster glass state below around 40 K: (i) a broad, frequency-dependent peak in the ac magnetic susceptibility, (ii) a slow relaxation of the magnetization, and (iii) a continuous increase in the dc magnetic susceptibility in field cooling process. The composition dependence of characteristic parameters for the cluster glass state suggests that chemical segregation can hardly explain the clustering mechanism. We propose a possible picture that the ferromagnetic clusters are distributed uniformly and form the glassy state embedded in the paramagnetic and metallic host of CaRuO3.

DOI： 10.7566/JPSJ.85.034711

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Publishing type：Research paper (scientific journal)  

© The Royal Society of Chemistry 2016. Systematic tuning of the ferroelectric phase transition in Bi2SiO5 was demonstrated using element substitution, where nominally heterovalent Pb was successfully substituted for Bi up to 20%. Comprehensive studies using powder X-ray diffraction analysis, dielectric measurements, X-ray absorption spectroscopy, and first-principles calculations revealed that charge compensation for heterovalent substitution was achieved via introduction of a considerable number of oxygen vacancies in Bi2O2 layers, resulting in the nominal composition (Bi1-x3+Pbx2+)2SiO5-x. The oxygen vacancies were found to induce local disordering of SiO4 tetrahedral chains, sandwiched between the Bi2O2 layers, leading to a decrease in the ferroelectric phase transition temperature and broadening of the phase transition in Bi2SiO5.

DOI： 10.1039/c6tc00584e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Systematic tuning of the ferroelectric phase transition in Bi2SiO5 was demonstrated using element substitution, where nominally heterovalent Pb was successfully substituted for Bi up to 20%. Comprehensive studies using powder X-ray diffraction analysis, dielectric measurements, X-ray absorption spectroscopy, and first-principles calculations revealed that charge compensation for heterovalent substitution was achieved via introduction of a considerable number of oxygen vacancies in Bi2O2 layers, resulting in the nominal composition (Bi1-x Pb-3+(x)2+)(2)SiO5-x. The oxygen vacancies were found to induce local disordering of SiO4 tetrahedral chains, sandwiched between the Bi2O2 layers, leading to a decrease in the ferroelectric phase transition temperature and broadening of the phase transition in Bi2SiO5.

DOI： 10.1039/c6tc00584e

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_2553

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_1859

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_2514

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_1494

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_2587

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_1002

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_1000

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

© 2015 The Physical Society of Japan. We report the effects of Ir impurity on the physical properties of Ba4Ru3-xIrxO10 (0 ≤ x ≤ 0.5) which is composed of three face-shared RuO6 octahedra (Ru trimer). We discuss the origin of the unique electronic phase transition from paramagnetic metal to antiferromagnetic insulator at 105K in terms of hybridized orbitals of Ru 4d in the Ru trimer. From the magnetic susceptibility and the specific heat, the transition temperature is found to decrease more remarkably than is expected in typical diluted magnets and is hardly discernible at around x = 0.5, while the magnetic interaction only decreases slightly with x. This implies that the transition is not driven by magnetic interaction. In contrast, the hump due to the phase transition still remains in the Seebeck coefficient for x = 0.5, which means that the charge gap still remains as a short-range order. Since the charge gap originates from the 4d hybridization in the Ru trimer, intra-trimer charge transfer is likely to dominate the transition.

DOI： 10.7566/JPSJ.84.094601

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Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

© The Royal Society of Chemistry 2015. Bismuth silicate (Bi2SiO5) was recently suggested as a potential silicate based lead-free ferroelectric material. Here, we show the existence of ferroelectricity and explore the strong anisotropy of local ferroelectricity using piezoresponse force microscopy (PFM). Domain structures are reconstructed using angle-resolved PFM. Furthermore, piezoresponse hysteresis loops and piezoelectric coefficients are spatially investigated at the nanoscale. The obtained results confirm the existence of ferroelectricity with strong c-axis polarization. These results could provide basic information on the anisotropic ferroelectricity in Bi2SiO5 and furthermore suggest its considerable potential for lead-free ferroelectric applications with silicon technologies.

DOI： 10.1039/c5nr03161c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

© 2015 Elsevier Ltd. Abstract Effects of element substitution on the phase transition between different pyroelectric phases of the stuffed-tridymite-type oxide, BaZnGeO4, are examined by dielectric measurements on BaZn1-xMxGeO4 (M=Ni, Co, and Mn) with x=0.05 and 0.10. The Ni2+-substitution is found to suppress strongly the phase transition, in marked contrast to the cases of Co2+ and Mn2+ that have only subtle influences on the transition temperature. Internal distortions of MO4 tetrahedra due to the Jahn-Teller effect might play a major role in the variation of transition temperature induced by the element substitution.

DOI： 10.1016/j.ssc.2015.06.011

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Language：English   Publishing type：Research paper (scientific journal)  

© 2015, The Korean Physical Society. We have investigated the structural changes and the microstructures of Ba1-xSrxAl2O4 for 0 < x < 0.4 by using transmission electron microscope (TEM) and synchrotron radiation powder X-ray diffraction experiments. The TEM experiments revealed the existence of a structural phase boundary at approximately x = 0.1, at which the superlattice reflection spots at the 1/2 0 0 -type positions change into diffuse streaks along three equivalent <110> directions in the hexagonal structure. In addition, real-space images of Ba1-xSrxAl2O4 for 0 < x < 0.4 reveal that BaAl2O4 should be characterized as a modulated structure with triple-q modulation vectors along the <110> directions and on the other hand, Ba1-xSrxAl2O4 for 0.1 < x < 0.4 be characterized as an intermediate (precursor) state with a rigid unit mode due to structural instability. These experimental results implied that the partial substitution of Sr2+ for Ba2+ should suppress a structural instability due to the AlO4 tetrahedral network and decrease the structural phase transition temperature.

DOI： 10.3938/jkps.66.1355

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

© 2015 The Japan Society of Applied Physics. To explore the thermoelectric transport nature of photo-excited carriers, the electrical conductivity and the Seebeck coefficient are measured under ultraviolet illumination in the wide-gap semiconductor ZnS near room temperature. The conductivity increases linearly as against the photon flux density with little dependence on temperature, indicating the conduction under illumination is mostly governed by the photo-doped carriers. We have found that, in high contrast to the temperature-insensitive photoconductivity, the temperature dependence of the Seebeck coefficient is dramatically varied by illumination, which is unexplained from a simple photo-doping effect for one majority carrier. Such a distinct difference in the transport quantities is rather understood within a two-carrier model, in which only the Seebeck coefficient is strongly affected by photo-excited minority carriers. The present result is also compared with earlier reports of the photo-Hall experiments to discuss the underlying photo-transport mechanism.

DOI： 10.7567/JJAP.54.031203

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

© 2015 The Physical Society of Japan. We have studied magnetic and transport properties in polycrystalline CaRu1-xScxO3 for 0 ≤ x ≤ 0.20 in order to clarify the substitution effects of a non-magnetic trivalent ion. We find that a ferromagnetic transition with Tc ~ 30K is observed in Sc-substituted samples. The composition dependence of the Curie-Weiss temperature ΘCW implies that the magnetic susceptibility has a paramagnetic contribution with negative ΘCW and a ferromagnetic contribution with positive ΘCW. The field dependence of magnetization at 2K is also understood as a summation of the ferromagnetic and paramagnetic components. These results suggest that CaRu1-xScxO3 is a non-uniform magnetic system. The relationship between the ferromagnetic ordering and the transport properties is also discussed.

DOI： 10.7566/JPSJ.84.014708

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Scopus

CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)  

We report the broadband light-scattering spectroscopy of a single crystal of a prototypical relaxor ferroelectric, Pb(Mg_1/3Nb_2/3)O₃. A self-similar, "power-law central peak" has been observed, indicating the presence of a fractal in the crystal. A strong correspondence exists between the temperature dependence of the power exponent, and that of the reported behaviors of "polar nanoregions", which consist of the fractal percolation cluster in the crystalline matrix of the material.

DOI： 10.5940/jcrsj.57.219

Language：English   Publishing type：Research paper (scientific journal)  

Phonon properties of lead titanate were investigated by measuring polarization-direction dependence of Raman intensities. Quantitative angle-resolved Raman spectroscopy is advantageous for detecting anisotropic nature of the sample material since that reflects the symmetry of vibrational modes. In this study, a broadband half-waveplate was utilized to establish high quantitativity, stability, and spatial reliability of the angle-resolved measurement.

DOI： 10.5940/jcrsj.57.285

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Ruthenium oxides are typical strongly correlated electron systems, where various ordering phenomena occur through delicate interplay among the charge, spin and orbital degrees of freedom. We propose that the thermoelectric properties can be improved by controlling such ordered phases in strongly correlated electron systems. Honeycomb Ru oxide Li2RuO3 is a prime example that exhibits a unique phase transition at 540 K with a charge gap. We have found that the ordered state can be modified by substituting the Ru site partially, and succeeded in increasing the thermopower by keeping the resistivity around the same value to enhance the power factor substantially.

DOI： 10.1039/c5tc01619c

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Publishing type：Research paper (scientific journal)  

© The Royal Society of Chemistry 2015. Ruthenium oxides are typical strongly correlated electron systems, where various ordering phenomena occur through delicate interplay among the charge, spin and orbital degrees of freedom. We propose that the thermoelectric properties can be improved by controlling such ordered phases in strongly correlated electron systems. Honeycomb Ru oxide Li2RuO3 is a prime example that exhibits a unique phase transition at 540 K with a charge gap. We have found that the ordered state can be modified by substituting the Ru site partially, and succeeded in increasing the thermopower by keeping the resistivity around the same value to enhance the power factor substantially.

DOI： 10.1039/c5tc01619c

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_2698

CiNii Books

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_2664

CiNii Books

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_2738

CiNii Books

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_2024

CiNii Books

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_2665

CiNii Books

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

© 2014 AIP Publishing LLC. We report photo-thermoelectric transport phenomena in Pb2CrO5 single crystals. Without illumination, this material exhibits an insulating behavior characterized by an activation-type temperature variation of the electrical conductivity. The Seebeck coefficient contrastingly shows a crossover from high-temperature insulating to low-temperature metallic behavior, which is attributed to degenerate carriers in a donor level. We have found that under illumination, both the conductivity and the Seebeck coefficient increase in magnitude with increasing photon flux density in the degenerate-conduction regime. This result is difficult to understand within a simple photo-doping effect, which usually leads to a decrease in the Seebeck coefficient under illumination. The observed phenomenon is discussed in terms of a two-carrier contribution to the transport properties.

DOI： 10.1063/1.4902248

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CiNii Research

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

© 2014 The Japan Society of Applied Physics. Crystal structures and microstructures in Ba1-xSrxAl2O4solid solutions between the end members of BaAl2O4 and SrAl2O4 have been carefully investigated by powder X-ray diffraction, electron diffraction and transmission electron microscopy (TEM) imaging experiments. With the help of fast Fourier transform (FFT) calculation, high-resolution TEM images suggested that diffuse streaks along three equivalent o110p directions in the (001) plane, which appear in the P63structure of Ba1-xSrxAl2O4for x = 0.4, originate from the large structural fluctuation of the AlO4 tetrahedral network. On the other hand, the monoclinic P21structure in Ba1-xSrxAl2O4with x = 0.7 was found to consist of a modulated structure with q - 0; 1=2; 0. The present experimental results reveal that a structural phase boundary exists at approximately x = 0.6 between the P63 structure with a large structural fluctuation and a monoclinic P21phase with the single-q modulated structure.

DOI： 10.7567/JJAP.53.09PB01

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We have investigated structural phase transition and changes of microstrucrtures in BaAl2O4 with the tridymite tetrahedral framework structure by transmission electron microscopy experiments in the temperature range between 100 K and 298 K. In our polycrystalline samples the transition from the paraelectric phase with the P6322 space group to the ferroelectric (FE) phase took place around 250 K, which ccompanie with the appearance of the modulated structure with the three equivalent modulation wave vectors, q = 1/2<100>. Real-space images revealed that the FE phase should consist of nanodomains with the 10 ∼ 20 nm size. In addition, it is revealed that partial substitution of Fe3+ for Al3+ in BaAl2O4 induced structural phase transition to themodulated structure with q = 1/3<110> around x ∼ 0.50 in Ba(Al 1-xFex)2O4.

DOI： 10.1080/00150193.2014.893160

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

© 2014 The Physical Society of Japan. We have prepared a set of single crystals of Ca3-xBixCo4O9 using a KCl/K2CO3 flux technique, and have measured the resistivity and Seebeck coefficient along the in-plane direction at low temperatures. In a single crystal of Ca2.8Bi0.2Co4O9, the resistivity reaches a value as low as 1mΩ cm at 70 K, where the mean free path is longer than the de Broglie length of the carrier. This clearly indicates that the non-metallic resistivity in Ca2.8Bi0.2Co4O9 is not due to carrier localization, which is seriously incompatible with a widely-accepted picture of this oxide. We have found that the low-temperature conductivity linearly changes with temperature below 20 K, and the observed temperature dependence is milder than that of the variable range hopping. We propose that this temperature dependence partly comes from pseudogap opening, i.e., anomalous suppression in the density of states.

DOI： 10.7566/JPSJ.83.054710

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Scopus

CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We have observed a persistent voltage oscillation induced by constant external electric fields in the nonmagnetic narrow-gap semiconductor SmS. This oscillation appears with a large nonlinear conduction in a relatively low electric field of a few kV/cm. We find that the oscillation frequency clearly changes on addition of an external capacitor parallel to the sample, indicating that the oscillation does not arise from the Joule heating effect. This oscillation is analyzed in terms of a carrier charging-discharging model, which is associated with an electric-field-induced insulator-to-metal transition as proposed in the oxide insulator VO2. This model reasonably explains the observed oscillation phenomenon, implying the existence of a possible instability toward a conductive state driven by the electric field. © 2014 American Physical Society.

DOI： 10.1103/PhysRevB.89.195103

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Recently, the mode splitting of B1+E in PbTiO 3-related heterostructures has been attracted wide range of attention because it is considered to represent intrinsic stress in the materials. However, the spectral behaviour of B1+E mods had remained unclear even in the bulk crystal, i.e., they had been often designated as "silent," even though they should be Raman active. This seems because they does not exhibit a significant mode splitting in the bulk crystal. This work employed an angle-resolved quantitative polarized spectroscopy to clarify the unclarity. The precise measurements revealed that the both two modes are ordinary Raman active modes with a minute energy difference. Copyright © 2014 Taylor & Francis Group, LLC.

DOI： 10.1080/00150193.2014.890470

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT UNION CRYSTALLOGRAPHY  

© © John C.H. Spence 2014. Electric dipole engineering is now an emerging technology for high electron-mobility transistors, ferroelectric random access memory and multiferroic devices etc. Although various studies to provide insight into dipole moment behaviour, such as phase transition, order and disorder states, have been reported, macroscopic spontaneous polarization has been mainly discussed so far. Here, visualization of the electric dipole arrangement in layered ferroelectrics Bi2SiO5 by means of combined analysis of maximum entropy charge density and electrostatic potential distribution analysis based on synchrotron radiation X-ray powder diffraction data is reported. It was found that the hierarchical dipole orders, the weak-ferroelectric and ferroelectric configurations, were observed in the Bi2O2 and the SiO3 layers, respectively, and the ferrielectric configuration was realised by the interlayer interaction. This discovery provides a new method to visualize the local polarization in ferroelectric materials.

DOI： 10.1107/S2052252514008008

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The photodielectric effect is demonstrated in Mott-insulator BaCoSiO 4 with a stuffed-tridymite-type structure under irradiation of visible light at 365 nm. The real part of dielectric permittivity is enhanced by ∼300% with little increase of tan δ in a low-frequency region. Results of diffuse reflectance spectroscopy, first-principles calculations and dielectric measurements suggest that the photodielectric effect stems from a response of photo-excited electrons in an unoccupied upper-Hubbard band for 3d-orbitals of cobalt, which have significantly small mobility due to the unique configuration of Co ions in the stuffed-tridymite-type structure. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4872032

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

I2-II-IV-VI4 quaternary Cu2ZnSn(S xSe1-x)4 (CZTSSe) alloys were successfully grown by the melting growth method. The powder X-ray diffraction (XRD) pattern of the CZTSSe alloys showed preferred orientations of (112), (220) and (312) planes, confirming the Kesterite structure. In Raman spectra, the A1 mode peaks expected for CZTS and CZTSe were observed in all samples, and no secondary phases were observed. The CZTSSe alloys in this study were slightly Cu-poor, Zn-rich and VI-rich, similar to compositions of polycrystalline thin-film materials that have achieved high photovoltaic conversion efficiencies. Single phase and homogeneous CZTSSe alloys were obtained. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2013.10.001

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

GaFeO3-type AlFeO3 is consisted of oxygen octahedra and tetrahedra containing Al and Fe ions and is known to have a non-centrosymmetric polar structure with space group Pna21. We tried to grow epitaxial GaFeO3-type AlFeO3 films on SrTiO 3 (111) substrates by pulsed laser deposition technique. Both the atomic arrangement of close-packed and the atomic distance of the substrate surface played important roles in stabilizing GaFeO3-type AlFeO 3 on the substrate. Piezoresponse force microscopy measurements clearly showed that GaFeO3-type AlFeO3 films have ferroelectricity at room temperature. In addition, AlFeO3 film also showed pinched-like hysteresis loop with TN ∼ 317 K. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4866798

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.69.1.3.0_550_1

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.69.2.3.0_350_3

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.69.2.3.0_285_3

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.69.2.4.0_693_3

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.69.2.4.0_680_3

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We report the observation of photo-Seebeck effect in tetragonal PbO crystals. The photo-induced carriers contribute to the transport phenomena, and consequently the electrical conductivity increases and the Seebeck coefficient decreases with increasing photon flux density. A parallel-circuit model is used to evaluate the actual contributions of photo-excited carriers from the measured transport data. The photo-induced carrier concentration estimated from the Seebeck coefficient increases almost linearly with increasing photon flux density, indicating a successful photo-doping effect on the thermoelectric property. The mobility decreases by illumination but the reduction rate strongly depends on the illuminated photon energy. Possible mechanisms of such photon-energy-dependent mobility are discussed. © 2013 AIP Publishing LLC.

DOI： 10.1063/1.4829460

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Scopus

Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We present a single-crystalline x-ray diffraction study on Ba4Ru3O10 consisting of corner-shared Ru3O12 trimers. The crystal structure is redetermined from 78 to 300K across an antiferromagnetic transition at 105 K. The orthorhombic symmetry (Cmca, space group No. 64) is preserved at all temperatures measured. This structure presents exceptionally long Ru-O distances characterized by a significant distribution within the Ru 3O12 trimer. A bond valence sum calculation suggests that the charge disproportionation within the Ru3O12 trimer emerges even at room temperature, which we ascribe to molecular orbital formation in the Ru3O12 trimer, as supported by the results of recent theoretical calculations. On the basis of the analyzed crystal structure, the electronic states and the nature of the phase transition at 105K are discussed. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.104603

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

A domain structure in periodically poled stoichiometric LiNbO3 was observed by confocal micro-Raman scanning spectroscopy. The 180°-domain, which is nominally invisible by Raman scattering due to equivalency of Raman selection rule for adjacent domains, was clearly visualized with a spatial resolution of 460 nm. At domain walls, an enhancement of Raman intensity was observed in optical modes that are closely related to the NbO bond, while there was no significant change in Li-ion related modes. NbO covalent bonds would be deformed by opposite ferroelectric displacements of ions across domain walls, to modify an electric polarizability of the Nb-ion related modes. © 2013 The Ceramic Society of Japan.

DOI： 10.2109/jcersj2.121.579

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A lead-free ferroelectric: The occurrence of ferroelectricity is demonstrated in a silicate-based compound (Bi2SiO5, see picture), by direct observation of polarization switching. The mechanism of ferroelectricity in Bi2SiO5 has been studied by Raman scattering, transmission electron microscopy, X-ray powder diffraction, and first-principles calculations. The observed ferroelectricity stems from twisting of the one-dimensional SiO4 tetrahedral chain. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/anie.201302188

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Scopus

PubMed

Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We investigated the growth condition of high-quality Cu 2ZnSnS4 (CZTS) single crystal by traveling heater method (THM) which is one of the solution-based growth methods. We selected Sn as solvent because it is a constituent element of CZTS with low melting point. The solubility of CZTS in Sn solvent was approximately 0.01 mol% at 600 °C and 0.28 mol% at 1000 °C. It is found that CZTS is soluble in Sn solvent, which is similar to CuGaS2 in In solvent. The Sn solutions saturated with CZTS solutes less than 60 mol% were separated with two phases, less than 30 mol% solutions were CZTS and Sn phases and solutions from 30 to 60 mol% were CZTS and SnSx compound phases. It is impossible to grow CZTS single crystal from less than 60 mol% Sn solutions, because secondary phases located at the bottom of the ampoule and interfered with single crystal growth. Optimum growth condition of CZTS was determined based on CZTS-Sn phase diagram, which was growth temperature 900 °C and X = 70 mol% solution. The electrical properties of CZTS single crystal were observed along the growth direction and it can be clearly seen that the electrical properties are homogeneous along the growth direction. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.201200815

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Ultrafast optical responses were investigated using a fs laser system on a layered perovskite-type cobalt oxide, La1.5Sr0.5CoO 4 with a checkerboard-type charge ordering. To investigate the spatial variation of the photoexcited state, we measured the transient changes of three independent optical quantities, i.e., transmittance, reflectivity, and backside reflectivity, as well as their fluence dependence at 0.25 eV. Using the numerical calculations based on Maxwell's equations, we calculated not only the dielectric constant but also the decay length of the photoexcited region (L) and analyzed the real-space dynamics of the photoexcited area in terms of the fluence and time dependence of L. With the above information on the time dependence of L and Kramers-Kronig analysis, we numerically calculated the transient optical conductivity spectra, which showed instantaneous formation of a polaron-like absorption peak in the midinfrared region. A 10 fs pump-probe reflection measurement revealed that the photoexcited state occurs within the time resolution (≈10 fs). The time profile of the reflectivity is accompanied with an oscillation assigned as a breathing phonon mode in the CoO2 layer observed in Raman spectroscopy. Analyses of the decay time and the frequency revealed that the photoirradiation melted the charge ordering in La1.5Sr0.5CoO4. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.074721

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CiNii Research

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

Electric field (E) control of the magnetic anisotropy and coercivity (HC) of a Fe film in Fe/BaTiO3 (BTO) is demonstrated at room temperature in the tetragonal phase of BTO. Polarizing microscopy and x-ray diffraction analysis of BTO (001) surface show distinctly two different regions; one with a1, a2 and c domains separated by 180° and 90° domain boundaries (DBs) (region 1) and the other with a1 domains separated by 180° DBs (region 2). The Fe film on region 1 shows complex magnetic anisotropy with the net magnetic easy axis in between [100] and [110] directions of BTO, while the magnetic anisotropy in region 2 exhibits two fold symmetry with an easy axis along [100]. In applied electric field (±10 kV/cm), the magnetic easy axis of the Fe film in region 1 is switched to the [110] direction of BTO, whereas in region 2 it stays unaffected. The HC versus E curves in region 1 show a butterfly-like behavior, while in region 2 no changes are observed. Also, the HC measured in E ±10 kV/cm at different magnetic field orientations shows dramatic changes in region 1 compared to region 2. The observed electric field dependent magnetic response in both regions can be understood based on the DBs modifications and associated strain effects. © 2013 American Institute of Physics.

DOI： 10.1063/1.4793511

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

An increase of the Curie temperature, TC, was demonstrated for BaTiO3 (BTO) epitaxial thin films grown by a pulsed laser deposition technique on (001) and (110) SrTiO3 (STO) substrates. The T C values for the BTO films on (001) and (110) STO were determined, from the temperature dependence of the lattice constants, to be 720 and 550 K, respectively, both of which are higher than that for bulk BTO. The increase of TC for the film on (001) BTO is suggested to stem from a large tetragonal deformation with a tetragonality of ∼1.02 due to a two-dimensional clamping effect, which persists even in the paraelectric phase. That for the (110) BTO film, on the other hand, could be caused by a one-dimensional clamping effect due to uniaxial strain. © 2013 IOP Publishing Ltd.

DOI： 10.1088/0953-8984/25/13/132001

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

An unconventional pseudo tetragonal crystal structure is demonstrated in a BaTiO3 (BTO) epitaxial thin film grown on a (110) SrTiO3 (STO) substrate by pulsed laser deposition. The crystal structure of the BTO film, one of whose principal axes is shorter than the other, is markedly different from the bulk tetragonal structure. The pseudo tetragonal structure would be caused by the nearly uniaxial strain due to the different strain relaxation along the [001] and [110] axes. An irregular 90 degrees domain structure observed by piezo response force microscopy (PFM) is understood on the basis of a possible small elastic strain at the domain boundary in the pseudo tetragonal crystal structure. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/APEX.6.015803

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Crystallographic Society of Japan  

An unconventional pseudo-tetragonal crystal structure is found in a BaTiO₃ epitaxial thin film grown on a （110）SrTiO₃ substrate. The unique crystal structure of the BaTiO₃ film, which is markedly different from the bulk tetragonal structure, is caused by the nearly uniaxial strain due to the different strain relaxation along ［001］ and ［1<span style="text-decoration: overline;">1</span>0］ axes.

DOI： 10.5940/jcrsj.55.290

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

Bismuth silicate Bi2SiO5 (BSO) nanoparticles were synthesized through a hydrothermal reaction followed by heat treatment. Kinds of characteristic methods were employed to study the phase, morphology and photophysical properties of BSO. The as-prepared BSO exhibited high photocatalytic activity and good photodegradation repeatability in the decomposition of Rhodamine B (RhB) dyes under simulated sunlight irradiation. The experimental results by using different scavengers demonstrate that the photogenerated h+ and e- radicals play an interactional role in the degradation of RhB dyes. BSO nanocrystals could be a promising photocatalysis in water purification industry. © 2013 Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.catcom.2013.04.029

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.68.2.4.0_650_3

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.68.2.3.0_583_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.68.1.4.0_1020_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.68.1.4.0_1033_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.68.1.3.0_581_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.68.1.4.0_1022_2

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report the high-resolution and broadband light-scattering spectroscopy of a single crystal of a prototypical relaxor ferroelectric, Pb(Mg 1/3Nb 2/3)O 3. A self-similar broad central peak, whose intensity is expressed as I(ω)∞ωα has been observed, indicating the presence of a fractal in the crystal. A strong correspondence exists between the temperature dependence of the exponent α and that of the reported behaviors of polar nanoregions. The estimated fractal dimension (d f≈2.6) at low temperatures clearly indicates a percolation transition of the polar nanoregions at around 240 K. © 2012 American Physical Society.

DOI： 10.1103/PhysRevLett.109.197601

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PubMed

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

<p>Ferroelectric material studies, e.g., those involving ferroelectric phase transition, structure and finite-temperature properties, using state-of-the-art first-principles calculations and experiments are described.</p>

DOI： 10.11470/oubutsu.81.9_760

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We investigated the pseudobinary phase diagram of the Cu 2ZnSnSe 4 (CZTSe)-Sn system in order to obtain the knowledge useful for the growth of high-quality CZTSe single crystals using a solution-based method. For Sn solutions saturated with less than ∼60 mol% CZTSe, the solutes are separated into two phases, whereas for Sn solutions with more than 60 mol% CZTSe, the solutes are of single phase. The CZTSe single crystals were obtained from a 80 mol% CZTSe solution (liquid temperature 850 °C) at 900 °C. The powder X-ray diffraction pattern of the CZTSe single crystal shows preferred orientations of (112), (220) and (312) planes, confirming the Kesterite structure of CZTSe. The Raman spectrum shows three peaks at 170, 193 and 231 cm -1, which correspond to CZTSe peaks. The composition of the CZTSe single crystal along the growth direction is found to be slightly Cu-poor, Zn-rich and Se-rich. Therefore, we obtained good-quality homogeneous CZTSe single crystal grown by Sn solutions. © 2012 Elsevier B.V.

DOI： 10.1016/j.jcrysgro.2012.05.030

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Ionic liquid-mediated vacuum deposition was demonstrated as a novel growth technique for high-quality C 60 crystallites. In this process the ionic liquid worked as a solvent, i.e. the gas phase C 60 precursors were continuously fed into the ionic liquid on a substrate in a vacuum chamber, from which the nucleation and the subsequent growth of C 60 crystallites proceeded. The impact of varying the substrate on the growth behaviour was intensively examined in terms of not only the lattice-mismatch between C 60 and the substrates, but also the wetting behavior of the ionic liquid on the substrates. This led to a significant improvement of the C 60 crystallinity and epitaxial growth was successfully found on certain substrates. In particular, molecularly smooth and thick C 60 hexagonal-shaped crystallites epitaxially grew on a MoS 2 substrate, the average size of which reached as large as 10 μm. © 2012 The Royal Society of Chemistry.

DOI： 10.1039/c2ce25163a

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We perform a Raman scattering study to elucidate the mechanism of temperature independent dielectric response of Ba 0.767Ca 0.233TiO 3 (BCTO-0.233) from a viewpoint of phonon dynamics. BCTO-0.233 remains tetragonal below T c down to 3.5 K. Over-damped soft phonon observed in a pure BaTiO 3 is found to become underdamped in BCTO-0.233, suggesting that local dipoles induced by Ca 2 off-centering suppress the hopping of Ti ions to reduce damping of the soft-mode. The temperature dependence of the soft-mode frequency agrees qualitatively with the dielectric permittivity through Lyddane-Sachs-Teller relationship, indicating that the dielectric response of BCTO-0.233 is governed by the soft-mode. © 2012 American Institute of Physics.

DOI： 10.1063/1.3693524

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

We investigated the phase diagrams of the Cu 2ZnSnS 4 (CZTS)Sn pseudobinary system in order to obtain knowledge useful for the growth of high-quality CZTS single crystals using a solution-based method. For Sn solutions saturated with less than ∼60 mol% CZTS, the solutes are separated into two phases (CZTS phaseSnS x phaseliquid phase). On the other hand, for solutions with more than 60 mol% CZTS, the solutes are single phase (CZTS phaseliquid phase). The CZTS single crystals were obtained from a 70 mol% CZTS solution (liquid temperature 850 °C) at 900 °C. The powder X-ray diffraction (XRD) pattern of the CZTS single crystal shows preferred orientations of (112), (220) and (312) planes, confirming the Kesterite structure of CZTS. The Raman spectrum shows three peaks at 287, 338, 371 cm -1, which corresponded to CZTS peaks. The composition of the CZTS single crystal along the growth direction is found to be slightly Cu-poor, Zn-rich and S-rich. Therefore, it is assumed that the Cu vacancy is the dominant p-type conduction mechanism. © 2011 Elsevier B.V.

DOI： 10.1016/j.jcrysgro.2011.12.046

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

An effect of Ca-substitution on ferroelectricity of CdTiO 3, whose paraelectric structure involves rotated oxygen octahedra, is studied by Raman scattering and first-principle calculations from a viewpoint of a relation between covalency and instability of lattice vibrations. Raman scattering experiments reveal that the Ca-substitution suppresses softening of a soft mode and reduces the phase transition temperature. An origin of the soft mode is elucidated by first principles calculations to be an asymmetric stretching of O-Cd-O bonds. The mechanism of Ca-induced suppression of the soft mode softening is clarified as follows: off-centering of Cd, which stems from freezing of the O-Cd-O asymmetric stretching vibration, is suppressed by the Ca-substitution through weakening of the covalency between Cd and O. The present results indicate that the covalency of ions plays a key role even in the perovskite-type oxides with pre-existing octahedral rotations. © Taylor & Francis Group, LLC.

DOI： 10.1080/00150193.2012.672035

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Crystallographic Society of Japan  

An Origin of ferroelectricity in Perovskite-type oxides is discussed from a viewpoint of relation between lattice dynamics and chemical bonding state, through comprehensive study of a Ca-substitution effect on the ferroelectricity in CdTiO₃. The result indicates covalency of constituent elements plays an important role on the ferroelectricity in the perovskite-type oxides.

DOI： 10.5940/jcrsj.54.276

CiNii Research

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

KH2PO4 (KDP) single crystals internally including an artificial isotope gradient are grown by a controlled solution-recrystallization method. The deuteron exchange rate of KDP single crystal is spatially tailored through crystal growth in a KD2PO4 (DKDP) saturated solution, where the deuteron concentration decreases with time. The position dependence of the deuteron concentration was precisely determined with confocal micro-Raman scanning giving a change in the Raman spectrum as a proof. The result indicates that the deuteron concentration continuously varies from 77 % to 7 % within 100 microns. Copyright © Taylor & Francis Group, LLC.

DOI： 10.1080/00150193.2012.743786

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Scopus

Other Link： http://orcid.org/0000-0003-3683-5416

Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

Photoluminescence properties of MgTiO3 thin film deposited by the pulsed laser deposition technique were investigated. Contrary to the spectrum for bulk MgTiO3, broad spectra around 605 nm was found to grow with the decrease of the target-substrate distance. The origin of the broad spectrum is discussed based on the defect chemistry of MgTiO3.

DOI： 10.14853/pcersj.2012S.0.192.0

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.67.1.4.0_997_4

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.67.1.4.0_997_3

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

A Cu2ZnSnS4 (CZTS) single crystal was grown at 900 °C, which is less than its melting point (962 °C) using a traveling heater method, which is one of the solution growth methods. No twins and no secondary phases could be distinguished from the Laue and X-ray diffraction patterns, respectively. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.50.128001

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

A mechanism for cation-substitution-induced suppression of ferroelectricity in a perovskite-type ferroelectric oxide, CdTiO3, has been elucidated in terms of the relationship between the covalency and the lattice dynamics. Raman scattering experiments and first-principles calculations clarified that a change in the covalency of Cd sites due to Ca substitution selectively decreases the frequencies of the modes associated with octahedral rotations whose axes are perpendicular to the spontaneous polarization direction. The resulting destabilization of zigzag octahedral chains synchronizes the hardening of the ferroelectric soft mode, which suppresses the ferroelectricity. This result enhances our understanding of the relationship between local chemical bonds and macroscopic ferroelectricity. © 2011 American Physical Society.

DOI： 10.1103/PhysRevB.84.174106

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

A mechanism for cation-substitution-induced suppression of ferroelectricity in a perovskite-type ferroelectric oxide, CdTiO3, has been elucidated in terms of the relationship between the covalency and the lattice dynamics. Raman scattering experiments and first-principles calculations clarified that a change in the covalency of Cd sites due to Ca substitution selectively decreases the frequencies of the modes associated with octahedral rotations whose axes are perpendicular to the spontaneous polarization direction. The resulting destabilization of zigzag octahedral chains synchronizes the hardening of the ferroelectric soft mode, which suppresses the ferroelectricity. This result enhances our understanding of the relationship between local chemical bonds and macroscopic ferroelectricity.

DOI： 10.1103/PhysRevB.84.174106

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

A combinatorial library of binary mixtures of ionic liquids with various mixing ratios was fabricated on a single sapphire substrate using the composition-spread technique combined with a continuous-wave infrared (CW-IR) laser deposition method; the mixtures were condensed in the form of micro-scale droplets. The mixing ratio within the droplets was examined by Raman spectroscopy. The contact angle of the droplets was found to systematically vary with the mixing ratio. Their thermal behavior was characterized with an ultrahigh-vacuum laser microscope, revealing the dependence of the evaporation rate on the mixing ratio. © 2011 National Institute for Materials Science.

DOI： 10.1088/1468-6996/12/5/054204

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Scopus

PubMed

Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

DOI： 10.1063/1.3643039

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

First-principles calculations of various phases of CdTiO3 carried out with the aim of obtaining insights into the mechanism of the ferroelectric phase transition and the structure of the low-temperature ferroelectric phase are reported. The results indicate that the preferred symmetry of the low-temperature phase is Pna21, rather than P2 1ma, corresponding to a small relative shift of the Ti and O ions in the paraelectric Pnma phase with the polarization axis parallel to the long axis. Calculated phonon dispersion curves show a distinct soft mode at the Γ point of the Pnma phase, which vanishes in the Pna21 phase, confirming that the transition to the ferroelectric phase is of the soft-mode displacive type. Calculations of perovskite CaTiO3, which also has an orthorhombic Pnma structure at room temperature but, unlike CdTiO3, does not exhibit a ferroelectric phase transition down to 4.2 K, were also carried out to help characterize the factors controlling ferroelectric phase transitions in perovskite titanates. © 2011 American Physical Society.

DOI： 10.1103/PhysRevB.84.104114

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We fabricated 18O-exchanged SrTi18O0.03x16O0.03(100-x) (STO18) thin films on SrTi 16O3(001) single-crystal substrates by pulsed laser deposition from a SrTi18O3 single-crystal target at various growth temperatures and 16O2 partial pressures. The diffusion of 16O from the substrate could be successfully suppressed by growing films under high 16O2 partial pressures, and a homogeneously 18O-exchanged STO18 thin film (x=60) was then obtained. The STO18 film became ferroelectric at a critical temperature higher than that expected from the corresponding STO18 bulk sample by ∼10 K, at which the Raman spectra suggested that the first-order transition occurred, different from the case of the STO18 bulk. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.4.091501

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

First-principles calculations of various phases of CdTiO3 carried out with the aim of obtaining insights into the mechanism of the ferroelectric phase transition and the structure of the low-temperature ferroelectric phase are reported. The results indicate that the preferred symmetry of the low-temperature phase is Pna2(1), rather than P2(1)ma, corresponding to a small relative shift of the Ti and O ions in the paraelectric Pnma phase with the polarization axis parallel to the long axis. Calculated phonon dispersion curves show a distinct soft mode at the Gamma point of the Pnma phase, which vanishes in the Pna2(1) phase, confirming that the transition to the ferroelectric phase is of the soft-mode displacive type. Calculations of perovskite CaTiO3, which also has an orthorhombic Pnma structure at room temperature but, unlike CdTiO3, does not exhibit a ferroelectric phase transition down to 4.2 K, were also carried out to help characterize the factors controlling ferroelectric phase transitions in perovskite titanates.

DOI： 10.1103/PhysRevB.84.104114

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Switching of the symmetry of magnetic anisotropy is clearly demonstrated in an epitaxial Fe layer on BaTiO3, in association with the interface lattice distortion occurred at the structural phase transition of BaTiO 3. The polar plot of the normalized remanent magnetization shows the fourfold symmetry with the magnetization easy axis along [100] of Fe at room temperature, while that at 230 K exhibits the twofold symmetry with the easy axis along [110]. Spatially resolved micro-Raman inspection corroborates the fact that the change in the magnetic symmetry arises from the magnetoelastic coupling at the interface. © 2011 American Institute of Physics.

DOI： 10.1063/1.3609237

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Scopus

Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We observed the evolution of polarization states and electromechanical coupling in (1 - x) AgNbO3-xNaNbO3 solid solutions using dielectric and strain hysteresis loop techniques and show that the polarization evolves from the ferrielectric ordering in AgNbO3 to the ferroelectric ordering in NaNbO3. The crossover between these two states occurs in the solid solution with x ≈ 0.8. A strain level ≈ 0.20 is available in the ceramics of these solid solutions. Such a large electromechanical effect might be interesting for the development of piezoelectric materials. © 2011 American Institute of Physics.

DOI： 10.1063/1.3609234

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

PMN relaxor is shown to be a nanosized ferroelectric from the polarization, lattice dynamics and transmission electron microscopic measurements. Its ferroelectric state broken in nanosized domains due to the quenched random field was clearly observed by aligning the domains along the same direction by a strong electric field for T<T_c〜225K. The reorientation of such nanosized domain is found to be essential for its giant dielectric response. In addition, a multiscale inhomogeneity of domain structure is found in the ferroelectric phase, in which many nanosized domains align together to form a single larger 'domain'.

DOI： 10.11316/butsuri.66.4_270

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Systematic Raman scattering experiments were performed on Pb(Mg 1/3Nb2/3)O3 (PMN) single crystals to resolve the low-wavenumber dynamics in the crystal. Careful checking of the angular dependence of the Raman spectra indicated that the intense peak around 45 cm-1, which always smears the low-wavenumber spectra, stems from the F2g mode due to Mg:Nb = 1:1 chemically ordered Fm3m region. A proper scattering configuration for eliminating the strong F2g mode allowed the observation of the lowest wavenumber soft mode dynamics in PMN. The results revealed the softening of the mode towards Tc with underdamped oscillation. The soft mode becomes overdamped in a wide temperature range above Tc, suggesting the development of cluster dynamics due to polar nanoregions. It recovers the underdamped oscillation and hardens in the high-temperature region. Finally, the physical picture of the relaxor phenomenon in PMN is discussed in terms of lattice dynamics by comparison with the typical displacive-type ferroelectric phase transition. A low-energy lattice dynamics in a typical relaxor ferroelectric material Pb(Mg1/3Nb 2/3)O3 (PMN) is investigated by Raman scattering spectroscopy. A rigorous optimization of Raman scattering configuration enables to detect a soft mode spectrum in PMN. Relaxor phenomenon is found to be triggered by the softening of the soft mode in an inhomogeneous system. Copyright © 2010 John Wiley & Sons, Ltd.

DOI： 10.1002/jrs.2746

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The ferroelectric property, crystal structure, and A1 (1TO) soft mode of almost strain-free epitaxial polar axis-oriented tetragonal lead zirconate titanate thick films grown on CaF2 substrates were investigated by changing the Zr/ (Zr+Ti) ratio and the temperature. The square of spontaneous polarization (Ps), Ps2, monotonically increased as tetragonal distortion, (c/a)-1, increased where a and c are the lattice parameters of the films and as the square of frequency in A1 (1TO), ω2 [A1 (1TO)], increased. Additionally, the relationships of Ps2, (c/a-1), and ω2 [A1 (1TO)] were experimentally obtained, which confirmed the P s value obtained from (c/a-1) and ω [A1 (1TO)] without direct polarization measurements. © 2011 American Institute of Physics.

DOI： 10.1063/1.3575565

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Phase evolution in (Ag1-xLix )NbO3 (ALN) solid solution was investigated by the x-ray diffraction technique, dielectric and polarization measurements. It is shown that a small substitution of Ag with Li gives rise to an orthorhombic-rhombohedral structural transformation in ABO3-perovskite silver niobate at room temperature. Structural refinements indicate that both the A- and B-site displacements contribute to the spontaneous polarization of the ferroelectric phase with symmetry R3c. Increasing Li-concentration enhances the ferroelectric rhombohedral distortion, resulting in an increase of the para-ferroelectric phase transition temperature and the polarization of the solid solutions. © 2011 IOP Publishing Ltd.

DOI： 10.1088/0953-8984/23/7/075901

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Scopus

PubMed

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

The low-frequency light-scattering spectrum in Pb(Mg1/3Nb 2/3)O3 single crystal is investigated at 297 K. A quasielastic scattering is found, and its line shape is identified as a "power-law" type, instead of a single Lorentzian or superposition of two Lorentzian curves. The power-law spectrum implies the existence of a wide distribution of relaxation times in relaxors. Copyright © Taylor &Francis Group, LLC.

DOI： 10.1080/00150193.2011.577365

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Scopus

Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

DOI： 10.14853/pcersj.2011F.0.626.0

Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

DOI： 10.14853/pcersj.2011F.0.286.0

Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

DOI： 10.14853/pcersj.2011F.0.320.0

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.66.2.4.0_974_4

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.66.1.4.0_960_3

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.66.1.4.0_972_1

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.66.1.4.0_970_4

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.66.1.4.0_969_4

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.66.1.4.0_969_3

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We propose a new approach to nanoscience and technology for ionic liquids (ILs): molecular beam deposition of IL in ultrahigh vacuum by using a continuous wave infrared (CW-IR) laser deposition technique. This approach has made it possible to prepare a variety of "nano-IL" with the given composition on the substrate: a nanodroplet, on one hand, the volume of which goes down to 1 aL and, on the other hand, an ultrathin film with a thickness to several 100 nm or less. The result of fractional distillation of a binary mixture of ILs, investigated by nuclear magnetic resonance as well as electrospray ionization time-of-flight mass spectrometry, indicates that this deposition process is based on the thermal evaporation of ILs, and thus this process also can be used as a new purification method of ILs in vacuum. Furthermore, the fabrication of binary mixture droplets of two ILs on the substrate by alternating deposition of two ILs was demonstrated; the homogeneity of the composition was confirmed even for one single droplet by high-spatial-resolution Raman spectroscopy. © 2010 American Chemical Society.

DOI： 10.1021/nn101036v

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The synthesis difficulty on AgTaO3 ceramic has been surmounted by the high oxygen-pressure sintering. In this study, the synthesized sample was investigated by both dielectric and micro-Raman measurements in detail. As no dielectric anomaly was observed between 2.2 and 694 K, the previously proposed ferroelectric phase transition from R3c to R 3̄ c at 170 K upon heating is not supported by our study whereas the quantum paraelectric ground state with R 3̄ c symmetry is more consistent with our experimental findings. Also, it is observed that the phase transition from this rhombohedral ground state to the higher-temperature monoclinic phase occurs at 667 K is purely soft-mode driven. Taking account the observation of additional Raman modes, at least up to 360 K, the existence of symmetry-breaking regions in the quantum paraelectric matrix is also discussed. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevB.81.104105

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Scopus

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

P-E hysteresis loop was measured for stoichiometric and non-stoichiometric NaNbO3. The untypical applied-field dependence of the hysteresis can be interpreted by the strong pinning effect on the domain reversal. The non-stoichiometry of the sample was found to enhance the pinning effect. It is finally concluded that NaNbO3 is intrinsically ferroelectric. © Taylor & Francis Group, LLC.

DOI： 10.1080/00150191003670408

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Scopus

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

The Raman scattering study was performed on BiFeO3 (BFO) both for polycrystal and single crystal forms. BFO was found to be easily damaged even by the weak power of the incident laser. The decomposition of BFO under the laser irradiation was investigated by examining the position dependence of the Raman spectrum over the irradiation area. Finally, we discuss the problem for the Raman measurement on BFO at the high-temperature region.

DOI： 10.1080/00150191003751422

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Scopus

Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

We performed a comprehensive investigation on the polarization evolution, lattice dynamics, and microscopic structural evolution of Pb(Mg1/3Nb2/3)O3(PMN) relaxor by polarization measurements, Raman scatterings and TEM. We find that the huge dielectric response in a broad temperature range in PMN can be attributed to the polarization reorientation effects. We also show that PMN relaxor is essentially a nanosized ferroelectric material with multiscale inhomogeneities of domain structure in addition to the well-known inhomogeneities of chemical composition and local symmetry.

DOI： 10.14853/pcersj.2010S.0.3A20.0

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.1.4.0_976_3

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.2.4.0_903_4

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.2.4.0_902_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.2.4.0_900_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.2.4.0_891_1

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.1.4.0_998_3

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.1.4.0_985_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.1.4.0_985_1

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.1.4.0_984_4

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.2.4.0_916_1

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Ferroelectricity has been induced in the quantum paraelectric AgTaO 3 (AT) by Li+ substitution, as evidence by both the dielectric anomaly and the hysteretic loop of electrical displacement versus applied electric field. The transition temperature (Tc) of Li-doped AT was found to increase with increasing level of Li+ substitution. Also, by substituting 12 mol % of Li+ into AT, which is close to the solubility limit, a ferroelectric material with a residual polarization ∼15 μC/ cm2 and Tc at 258 K was then triggered. © 2009 American Institute of Physics.

DOI： 10.1063/1.3275750

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Despite intensive studies on Pb(Mg1/3Nb2/3)O3 (PMN) relaxor, understanding the exact nature of its giant dielectric response and of its physical ground state is a fundamental issue that has remained unresolved for decades. Here, we report a comprehensive study of PMN relaxor crystal, and show that (i)its anomalous dielectric behavior in a broad temperature range results from the reorientation of polarization in the crystal, and (ii)the PMN relaxor is essentially a nanosized ferroelectric material with multiscale inhomogeneities of domain structure in addition to the well-known inhomogeneities of chemical composition and local symmetry. Such inhomogeneities are believed to play a crucial role in producing the huge and enigmatic physical effects in relaxor system, and may be used to design other new systems with giant effects such as a relaxor system. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevLett.103.207601

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The structures of glassy and metastable crystalline BaTi2O5 fabricated by the containerless method were comprehensively investigated by combined X-ray and neutron diffractions, XANES analyses, and computer simulations. The three-dimensional atomic structure of glassy BaTi 2O5 (g-BaTi2O5), simulated by Reverse Monte Carlo (RMC) modeling on diffraction data, shows that extremely distorted TiO5polyhedra interconnected with both corner- and edge-shared oxygen formed a higher packing density structure than that of conventional silicate glass linked with only corner-sharing of SiO4 polyhedra. In addition, XANES measurement revealed that five-coordinated TiO5 polyhedra were formable in the crystallized metastable α- and β-BaTi2O5 phases. The structure of metastable β-BaTi2O5 was solved by ab initio calculation, and refined by Rietveld refinement as group Pnma with unit lattices a = 10.23784(4) A, b = 3.92715(1) A, c = 10.92757(4) A. Our results show that the glass-forming ability enhanced by containerless processing, not by "strong glass former", fabricated new bulk oxide glasses with novel structures and properties. © 2009 American Chemical Society.

DOI： 10.1021/cm802483w

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Scopus

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

The light scattering spectra of the lowest frequency polar mode in the oxygen-isotope induced ferroelectric SrTi18O3 were observed in both paraelectric and ferroelectric phases. A perfect softening of the Eu mode at the phase transition is observed by the high-resolution spectroscopy in terms of the Fabry-Perot interferometry. The Raman-inactive polar modes are activated by the local symmetry breaking in the centrosymmetric tetragonal-paraelectric phase. The phase transition mechanism is a perfect displacive type in agreement with the theoretical studies. Both of the perfect softening and the dynamic inhomogeneity enhanced near the critical concentration play an essential role in the oxygen-isotope induced phase transition of SrTi18O3. Copyright © Taylor & Francis Group, LLC.

DOI： 10.1080/00150190902852117

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Scopus

Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

DOI： 10.14853/pcersj.2009F.0.1PA34.0

Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

DOI： 10.14853/pcersj.2009S.0.166.0

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We report that the orthorhombic-rhombohedral phase transition temperature in sodium potassium niobate could be tuned from lower to higher than room temperature by incorporating barium zirconate into it. It is revealed that when barium zirconate is between 8 mol% and 15 mol%, the solid solution exhibits rhombohedral symmetry at room temperature. Rietveld analysis shows that the space group of the rhombohedral phase is R3m. It is suggested that a relatively larger B-cation favors the low-temperature phase which is a common phenomenon for perovskite ferroelectrics. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssr.200903090

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Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

DOI： 10.14853/pcersj.2009F.0.1G20.0

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.64.2.4.0_885_4

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.64.1.4.0_984_3

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.64.1.4.0_951_3

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.64.2.4.0_680_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.64.2.4.0_887_2

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.64.2.4.0_886_3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The soft mode behavior in PbTiO3 (PT) single crystal has been revisited by our confocal micro-Raman measurements. Contrary to the common understandings, the temperature dependence of soft mode in the cubic PT paraelectric phase was precisely resolved for the first time, owing to the existence of macroscopic size Raman active regions (≥780 nm). By evidently ruling out the possibility of defect-induced Raman scattering, the elasto-optical coupling serves as the most likely mechanism for the occurrence of these Raman active regions. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.78.172103

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/cm801905d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Cadmium pyroniobate (Cd2 Nb2 O7: CNO) is a recent focus in the ferroelectric materials due to its unusual diffuse-phase transition without any compositional fluctuation, unlike conventional relaxors. In the present study, the critical dynamics of CNO was studied by the confocal micro-Raman scattering. The heavily overdamped soft-mode spectra have been resolved in the ferroelectric phase. The coupled-mode analysis successfully extracted the contribution of the relaxational mode from the overdamped soft mode. The decomposed soft mode clearly shows the Landau-type critical behavior with γ=1. The relaxation was reasonably assigned to the hopping motion of Cd ions from its activation energy of ∼21 meV. The phase transition of CNO, in spite of diffusive characteristics in the dielectric peak, is concluded to be purely driven by the conventional softening of the soft mode, which is heavily overdamped due to the coupling with Cd-hoping mode. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.77.224104

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Local probing of conduction behaviors using atomic force microscopy clearly shows that the grain boundary of polycrystalline CaCu3Ti 4O12 is semiconducting. In contrast, the grain is a mixture of semiconducting and insulating regions. This inhomogeneous conductive feature leads to giant dielectric response in CaCu3Ti 4O12. Theoretical analysis demonstrates that the dielectric response follows a typical Debye-type relaxation, and its unusual temperature dependence originates from the thermal activation behavior of free carries within the semiconducting regions in the grain. An effective way to control the electrical properties of CCTO is to control the defect density within a grain rather than the grain boundary. © 2008 American Chemical Society.

DOI： 10.1021/cm0710507

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Non-isothermal crystallization process of ferroelectric-based BaTi2O5 glass (BTO-glass) is investigated by in situ Raman scattering. The gradual change of Raman spectra clearly shows the successive crystallization of BTO-glass through metastable α and β phases. The increase of volume fractions obtained from the development of spectral intensities is analyzed by the Johnson-Mehl-Avrami formula. The results indicate homogeneous crystallization of α phase and subsequent inhomogeneous crystallization of β phase. Finally specially resolved observation reveals the phase separation of β phase on the surface and BaTi2O5 crystal phase in the inside. © 2007.

DOI： 10.1016/j.mseb.2007.09.030

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

Ferroelectric phase transition of 18O-exchanged SrTiO 3 (STO18) was investigated by Raman scattering as a function of the isotope exchange rate x. The result reasonably indicates the existence of the ideal soft mode-type quantum ferroelectric phase transition in STO18. In the vicinity of the critical concentration (xc = 33%), the coexistence of the paraelectric and ferroelectric regions was newly found, in drastic contrast to the homogeneous ferroelectric phase transition in the strongly exchanged STO18, whose x is sufficiently larger than xc. Near xc, the softening of the soft mode shows unusual rounding as a result of the coexistence. The present result indicates novel phase transition nature in the quantum ferroelectric phase transition of STO18, where dynamic heterogeneity plays an essential role.

DOI： 10.1080/00150190802371242

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.63.1.4.0_944_2

CiNii Research

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

Ferroelectricity in perovskite-related oxides was briefly reviewed mainly from the view point of crystal chemistry. Tolerance factor, t, for perovsikte oxides clearly discriminates the dielectric properties of them, except for KTaO. B-site off-center and BO6 tilting become dominant for t > 1 and t < 1, respectively. Only BaZrO3 and SrTiO3 sit on t = 1.00. A-O covalent bonding seems essential for the evolution of ferroelectricity in ABO3 perovskites, especially for the compounds with t < 1.

DOI： 10.1080/00150190802377918

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.77.224104

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Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

DOI： 10.14853/pcersj.2008F.0.184.0

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We report the growth and the piezoelectric properties of lead-free perovskite single crystals of Ag1-x Lix Nb O3. It possesses a rhombohedral structure with high ferroelectric phase transition (Tc =548 K for x=0.086) and large spontaneous polarization (Ps ∼40 μC cm2 for x=0.062) along the 〈111〉c direction of pseudocubic perovskite structure for x>0.05-0.06. High quasistatic d33 ∼210 pCN and low dielectric constant have lead to a very large value of piezoelectric voltage constant g33 ∼53.9× 10-3 VmN for the 〈001〉c -cut crystal of this simple perovskite. It has been shown that Li substitution might enhance the piezoelectric coefficient of the crystal. The excellent piezo-/ferroelectricity of this system are considered to be facilitated by the strong polarization nature of both Ag and Li in the perovskite structure. Our findings may stimulate further interests in the development of lead-free piezoelectrics. © 2008 American Institute of Physics.

DOI： 10.1063/1.2918837

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

Raman scattering of lead nickel niobate Pb(Ni1/3Nb 2/3)O3 (PNN) single crystals grown by the flux method has been performed to investigate the temperature dependence of the optical phonons of relaxors. Anomaly of the temperature dependence of the Raman intensity at 780 cm-1 was observed. Polar microregions promote the growth of volume gradually above the Curie temperature (∼170 K), and then freeze around 200 K. From the extrapolation of the temperature dependence of the depolarization ratio, we tried to estimate Burns temperature.

DOI： 10.1080/00150190802365962

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.63.2.4.0_870_4

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.63.2.4.0_884_2

CiNii Research

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The ferroelectric phase transition and the critical soft-mode behavior of CdTi O3 were investigated by confocal micro-Raman scattering. The soft mode softens toward zero frequency at Tc with the underdamped vibrational state, indicating ideal displacive-type ferroelectric phase transition. The continuous development of the spectra of ferroelectric modes clarified the second-order phase transition of CdTi O3. The soft mode undergoes an unusual splitting during the softening, which is reasonably explained by anticrossing between the soft mode and the different symmetry mode due to the local symmetry breakdown into the triclinic one. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevB.76.212103

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The ferroelectric phase transition and the critical soft-mode behavior of CdTiO3 were investigated by confocal micro-Raman scattering. The soft mode softens toward zero frequency at T-c with the underdamped vibrational state, indicating ideal displacive-type ferroelectric phase transition. The continuous development of the spectra of ferroelectric modes clarified the second-order phase transition of CdTiO3. The soft mode undergoes an unusual splitting during the softening, which is reasonably explained by anticrossing between the soft mode and the different symmetry mode due to the local symmetry breakdown into the triclinic one.

DOI： 10.1103/PhysRevB.76.212103

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

New features of the ferroelectric phase transition are found by using light scattering studies on quantum paraelectric SrTi16O3 (STO16) and its oxygen-isotope exchanged compound SrTi18O3 (STO18). The ferroelectric Eu mode observed by using high-resolution spectroscopy with interferometry shows a perfect softening at the phase transition point of the ferroelectric STO18-95, where 95 % of the oxygen atoms are replaced by the oxygen isotope 18O. The phase transition is concluded to be an ideal displacive-type transition accompanied with the complete freezing of the Slater-type polar mode. The role of the substituted 18O atoms is elucidated in more detail by using low-frequency Raman scattering below 1 K with a triple monochromator. The dynamical inhomogeneity enhanced by the inhomogeneous distribution of 18O atoms plays an essential role in quantum paraelectric STO18 where the concentration of 18O is less than the critical value of 33 %. Both the decrease in the frequency of the polar modes as a mass effect and the enhancement of the dynamical inhomogeneity take place cooperatively in the quantum paraelectric-ferroelectric phase transition in STO18.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The quantum ferroelectric phase transition of O18-exchanged SrTiO3 (x% exchanged SrTiO3 is abbreviated as STO18-x) was investigated by Raman scattering as a function of x. The result indicates the ideal soft mode-type quantum ferroelectric phase transition of STO18-x, where the O18 exchange enhances the softening of the soft mode by the suppression of quantum fluctuation. In the vicinity of the quantum critical point (x∼xc=33%), the system results in the ferroelectric-paraelectric phase coexistence state, in clear contrast to the homogeneous ferroelectric phase in STO18-x, whose x is sufficiently larger than xc. Simultaneously, the softening of the soft mode becomes strongly rounded with the underdamped oscillation. The present result indicates that the sensitivity of the soft phonon vibration to the mass disorder is dramatically enhanced in the vicinity of the quantum critical point. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevLett.99.017602

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PubMed

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

Recent light scattering studies on the oxygen-isotope exchanged strontium titanate SrTi18O3 (STO18) have reported a new feature of the ferroelectric phase transition; a perfect softening of the polar E u mode at TC has been found in 95% exchanged STO18 by a high-resolution interferometric spectroscopy. The frequency of the polar E u mode becomes zero at TC without any anomalous increase of the attenuation. The phase transition mechanism is an ideal displacive type induced by the instability of the Slater-type polar mode. The Raman scattering at ultra-low temperature using the 3He cryostat elucidates importance of inhomogeneity enhanced by the distribution of 18O atoms in STO18-x, where x is the concentration of 18O.

DOI： 10.1080/00150190701515790

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.62.2.4.0_996_1

CiNii Research

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

Dense polycrystalline samples of CaCu3Ti4O12 (CCTO) were prepared by solid-state reaction method under a high hydraulic pressure of 700 MPa, and characterized by X-ray diffraction, scanning electron microscopy and atomic force microscopy (AFM). Probing of the conduction path in nanoscale by AFM reveals that the grain boundary layer is conductive in CCTO. Therefore, reported giant-dielectric response in CCTO can not be understood by the model of conducting grains surrounded by insulating grain boundaries, which is usually used for the explanation of conventional internal barrier layer capacitors.

DOI： 10.1080/00150190601187500

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Polarization measurements reveal that AgNbO3 has an extremely large polarization, which can reach a value of 52 μC/cm2 in polycrystals. Experiments also show that the large internal atom distortion in AgNbO3 is also strongly coupled to the electric field, indicating that high piezoelectric performance can be realized in AgNbO3 system. This finding opens the way to designing a new class of lead-free, high-performance piezoelectric materials based on AgNbO3. ©2007 American Institute of Physics.

DOI： 10.1063/1.2751136

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Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

DOI： 10.14853/pcersj.2007F.0.503.0

Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER-VERLAG BERLIN  

Typical quantum paraelectric SrTiO3 becomes quantum paraelectric by oxygen isotope exchange. Apparently the change in the Curie temperature Tc is explained by the criteria of the theory for quantum ferro/paraelectrics. Tc for an isotope-exchanged sample depends only on the average mass of oxygen. Ferroelectricity for the oxygen isotope-exchanged SrTiO3 results mainly from the condensation of the Slater-type soft mode. However, an order-disorder component exists in addition to the displacive soft mode component. Raman spectra and NMR results suggest that ferroelectric domains do not develop through the crystal-like normal ferroelectrics. The role of the lattice defect must be elucidated and related to the phase transition mechanism in future works. Oxygen isotope exchange is considered the best way to understand the phase transition mechanism of SrTiO3 because this exchange may not accompany the formation of random fields or defects. © Springer-Verlag Berlin Heidelberg 2007.

DOI： 10.1007/430_2006_046

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Language：English   Publishing type：Research paper (international conference proceedings)  

Quantum paraelectric SrTiO 3 shows the ferroelectricity by the exchange of 16 O for its isotope 18 O. Raman scattering experiment is performed on the isotopically exchanged SrTi(O 0.32 16 18 O 0.68 ) 3 whose exchange rate is just below the critical exchange rate. Raman spectrum of ferroelectric soft mode in the paraelectric phase clearly indicates local symmetry-breaking induced by the 18 O-exchange. The temperature dependence of the soft mode in SrTi(O 0.32 16 18 O 0.68 ) 3 suggests the occurrence of local ferroelectric region before the onset of the ferroelectric phase. The inhomogeneity of the system induces the inhomogeneous softening of the soft mode in 18 O-exchanged SrTiO3.

DOI： 10.1080/00150190600738196

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/cm0525555

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DOI： 10.1007/BF02679539

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Raman scattering spectra of the superionic-conductive lithium tetraborate Li2B4O7 are observed in the frequency range between 0-1600cm-1 as a function of temperature from 4.2K to room temperature. The frequencies of four Raman active AI (TO) modes of 262, 353, 378, and 423 cm-1 at 4.2 K are newly assigned to be related closely with the motion of the Li-ions in superionic conduction. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.152

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Organizing Committee of Russia/CIS/Baltic/Japan Symposium on Ferroelectricity  

DOI： 10.11533/rcbjsf.2006.0.42.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Organizing Committee of Russia/CIS/Baltic/Japan Symposium on Ferroelectricity  

DOI： 10.11533/rcbjsf.2006.0.3.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Organizing Committee of Russia/CIS/Baltic/Japan Symposium on Ferroelectricity  

DOI： 10.11533/rcbjsf.2006.0.80.0

CiNii Research

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Ferroelectric phase transition of quantum paraelectric SrTiO3 is induced by an exchange of O-16 for its isotope O-18 in a low temperature region. The dynamics of ferroelectric soft mode in weakly O-18-exchanged strontium titanate is studied by Raman scattering. A nominally Raman-inactive soft mode is observed in the paraelectric phase of SrTi((O0.32O0.68)-O-18-O-16)(3) due to the local symmetry-breaking. The observed soft mode spectrum shows the temperature dependence strongly affected by the inhomogeneity of the system. The soft mode nonuniformly freezes to induce the local ferroelectric order before the onset of ferroelectric phase. The dynamical inhomogeneity is concluded to play an essential role in the dielectric response of O-18-exchanged strontium titanate.

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Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan  

DOI： 10.14853/pcersj.2006F.0.19.0

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The oxygen isotope effect on the soft-mode dynamics in quantum paraelectric SrTi (Ox18 O 1-x 16) 3 [STO18- x] is investigated by Raman scattering in terms of local symmetry breaking in the paraelectric phase. The exchange rates x of the O18 atoms are 0.23 [STO18-23] and 0.32 [STO18-32], which are less than the critical value xc (=0.33). In STO18-32, whose exchange rate is just below xc, the soft Eu mode shows hardening behavior in a low-temperature region indicating the onset of local ferroelectric order. On the other hand, the soft Eu mode in STO18-23 does not show any hardening behavior until 0 K. The enhancement of the inhomogeneity in the crystal by the exchange of O18 is concluded to play an essential role in the soft-mode dynamics of the quantum paraelectric and ferroelectric STO18- x. The relation between the soft-mode dynamics and quantum fluctuation is discussed. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.72.064111

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.60.2.4.0_803_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.60.1.4.0_913_3

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.60.1.4.0_890_4

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Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The ferroelectric microregion (FMR) in quantum paraelectric SrTiO 3 is studied by Raman scattering using an optical cryostat with a 3He refrigerator. By the partial exchange of the oxygen atom for its isotope 18O, broad FMR spectra change drastically to underdamped Lorentzian-type spectra with decreasing temperature below 10 K. The peak is assigned to the ferroelectric soft Eu mode. The intense and sharp spectra of the Eu mode, which are nominally Raman inactive, indicate that the symmetry is lowered to a non-centrosymmetric symmetry in FMR. Furthermore, the softening characteristic of the soft Eu mode in a low-temperature region implies that the symmetry is not necessarily ferroelectric. The local symmetry breaking is enhanced by the substitution of the isotope 18O. © 2004 The Physical Society of Japan.

DOI： 10.1143/JPSJ.73.3262

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Publishing type：Research paper (scientific journal)   Publisher：一般社団法人日本物理学会  

Crystal structure of deuterated glycinium phosphite was studied in the paraelectric (P) phase at 348 K and in the ferroelectric (F) phase at 223 K by means of the single crystal neutron diffraction. Deuteration rate is estimated to be 0.939 by the least-squares refinement. In the P phase, quasi-one-dimensional hydrogen bond chains are built by mutually linking the DPO^<2->_3 anions through two different types of hydrogen bonds with the bond angles of 179.2 and 171.6°. Two independent deuterons within the hydrogen bonds forming the chains are disordered over two sites separated by 0.545 and 0.539 Å. In the F phase, they order at a position nearly equal to one of two sites related by the disorder in the P phase. With the ordering of the deuterons, the P-O bonds with covalently bonded deuteron elongate, and those without covalently bonded deuteron reduce their lengths to some extent from the values determined in the P phase. Two oxygens involved in the hydrogen bond with the bond angle 179.2° exhibits especially large displacements in the F phase. This suggests strongly an importance of this hydrogen bond in the polarization appearance and in the ferroelectric transition. Comparison with results of non-deuterated salt indicates that only the hydrogen bonds forming the chains show significant isotope shift. In particular, the hydrogen bond with the bond angle 179.2° exhibits the most pronounced shift on the angle parameter defined by the angle between the line connecting two sites of disordered proton or deuteron and the line connecting two oxygens involved in the hydrogen bond.

Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Language：English   Publishing type：Research paper (scientific journal)  

Crystal structure of deuterated glycinium-phosphite was studied in the paraelectric (P) phase at 348 K and in the ferroelectric (F) phase at 223 K by means of the single crystal neutron diffraction. Deuteration rate is estimated to be 0.939 by the least-squares refinement. In the P phase, quasi-one-dimensional hydrogen bond chains are built by mutually linking the DPO32- anions through two different types of hydrogen bonds with the bond angles of 179.2 and 171.6°. Two independent deuterons within the hydrogen bonds forming the chains are disordered over two sites separated by 0.545 and 0.539 Å. In the F phase, they order at a position nearly equal to one of two sites related by the disorder in the P phase. With the ordering of the deuterons, the P-O bonds with covalently bonded deuteron elongate, and those without covalently bonded deuteron reduce their lengths to some extent from the values determined in the P phase. Two oxygens involved in the hydrogen bond with the bond angle 179.2° exhibits especially large displacements in the F phase. This suggests strongly an importance of this hydrogen bond in the polarization appearance and in the ferroelectric transition. Comparison with results of non-deuterated salt indicates that only the hydrogen bonds forming the chains show significant isotope shift. In particular, the hydrogen bond with the bond angle 179.2° exhibits the most pronounced shift on the angle parameter defined by the angle between the line connecting two sites of disordered proton or deuteron and the line connecting two oxygens involved in the hydrogen bond. ©2004 The Physical Society of Japan.

DOI： 10.1143/JPSJ.73.107

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.59.2.4.0_867_2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：THE PHYSICAL SOCIETY OF JAPAN  

Crystal structure of H3NCH2COOH·H 2PO3 was studied in the paraelectric phase (P phase) at 298 K and in the ferroelectric phase (F phase) at 170 K by means of the single crystal neutron diffraction. Two independent protons in the hydrogen bonds forming the H(HPO3)- chains are disordered over two sites with the separations of 0.486(3) and 0.474(5) Å in the P phase. In the F phase, they are ordered at a position nearly equal to one of two sites related by the disorder. With the proton order, lengths of the P-O bonds with the oxygens involved in the hydrogen bonds forming the chain deviate from their values determined in the P phase. A possible mechanism for the appearance of the spontaneous polarization is discussed in connection with the deformation of the HPO32- anions in the F phase. © 2003 The Physical Society of Japan.

DOI： 10.1143/JPSJ.72.1111

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