記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Applied Electronic Materials  

Doping of a small amount of La3+ into ferroelectric Bi2SiO5 induces the disorder of SiO4 chains in its crystal structure, leading to a transition into a paraelectric phase with a superior temperature stability of the dielectric permittivity. In this study, we attempted to fabricate bulk La-doped Bi2SiO5 ceramics through sintering with the aim of applying Bi2SiO5 to ceramic capacitors. (Bi1-xLax)2SiO5 fine powders with a La content x of up to 0.05 were synthesized by a sol-gel method and then sintered at low temperatures below 740 °C. The undoped Bi2SiO5 decomposed into secondary phases after sintering at temperatures over 640 °C due to its metastable nature, whereas La doping retarded the thermal decomposition, enabling sintering at higher temperatures. As a result, high relative densities near 90% were achieved for (Bi1-xLax)2SiO5 ceramics with x = 0.03 and 0.05 without the formation of secondary phases. The dielectric peak due to the ferroelectric-paraelectric phase transition at around 400 °C disappeared with the increase in La content. The obtained (Bi0.97La0.03)2SiO5 ceramic consequently exhibited a temperature-stable dielectric permittivity over a wide temperature range between −160 and 500 °C. A highly linear large-field dielectric response of the (Bi0.97La0.03)2SiO5 ceramic was observed under varying electric fields up to 220 kV cm-1 (at 20 °C) and at varying temperatures between −60 and 60 °C (at 100 kV cm-1).

DOI： 10.1021/acsaelm.3c00586

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry C  

Co-doping of heterovalent ions to rutile-type TiO2 has recently attracted attention as a new concept for designing high-permittivity materials with local structure engineering. However, the role of co-dopants in permittivity enhancement remains an open question. In the present study, dielectric measurements are performed in Nb + X (X = Al, Ga, In) co-doped and Nb-doped rutile-type TiO2 single crystals before and after annealing in X2O3 powders. The apparently huge permittivity, on the order of 105, is observed in all as-grown samples. Systematic analyses of dielectric relaxation observed in the as-grown samples clarify that thermally excited carriers render the sample semiconducting, thus giving rise to the apparently huge permittivity. In the post-annealed samples, in contrast, the huge permittivity disappears, and the dielectric loss markedly decreases to indicate recovery of the insulating property. X-ray fluorescence analyses show that the insulation recovery stems from migration of X cations into the single crystal, which is caused by the post-annealing. The post-annealing time dependence of the dielectric properties indicates that minute control of the Nb-to-X ratio is crucial for simultaneously achieving both the large permittivity and the fine insulating property in the co-doped TiO2. The present results offer an important clue toward clarifying the mechanism of permittivity boosting in co-doped TiO2

DOI： 10.1039/d2tc03914a

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

Hyper-ordered structures (HOSs) form through a synergy between local imperfections like defects or impurities and a surrounding environment around them, to give rise to emergent functionalities that can never be obtained with the local structures or homogeneous bulk materials alone. Typical examples are ensembles of heterovalent ionic substituents and the related ionic vacancies for charge compensation. Enhanced properties are often electrical in nature, such as improved permittivity, breakdown strength, and energy storage efficiency. In this work we overview HOSs in ferroelectric and dielectric materials from conventional to newly proposed ones and discuss their potential to design innovative next-generation materials for dielectric and energy storage applications.

DOI： 10.7566/JPSJ.91.091001

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Materials  

A phase variation of a pseudo-Roddlesden-Popper-type ferroelectric oxide Li2Sr1-xCax(Nb1-xTax)2O7 is systematically investigated using dielectric measurements, second harmonic generation, and x-ray diffraction experiments. We find an exotic x-T phase diagram, including paraelectric Cmcm, antiferroelectric Pmcn, and in-plane antiferroelectric and out-of-plane ferroelectric P21cn phases. At low x, we observe large and divergent dielectric anomalies associated with phase transitions from Cmcm to P21cn, whereas these become small kinks at high x. Structural analyses reveal an internal distortion, and the rotation of octahedra strongly depends on x, which is consistent with the lattice dynamics obtained by a density functional theory calculation. These results demonstrate the great tunability of dielectric properties in layered perovskite-type oxides by tuning the chemical bonding state in the octahedron.

DOI： 10.1103/PhysRevMaterials.6.044412

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

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

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry C  

The dielectric and piezoelectric properties of aluminate-sodalite-type oxides, (Ca1-xSrx)8[AlO2]12{MoO4}2 ((CS)AM-x), have been investigated in the present study. The variation of dielectric anomalies clarifies the phase diagram of (CS)AM-x over a composition range of x = 0.00-0.20 to suggest that a unique phase boundary like the morphotropic phase boundary (MPB) exists between x = 0.05 and 0.10. The piezoelectric voltage coefficient g33 at room temperature has been found to culminate around the phase boundary with the value being greater than that for the conventional lead-free perovskite-type ferroelectric oxides. The present result sheds light on the development of eco-friendly piezoelectric-active materials with excellent functionalities.

DOI： 10.1039/d1tc03897d

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

DOI： 10.7566/jpsj.90.114706

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JPhys Energy  

Thermoelectric properties of single crystal Ta2PdSe6 is investigated by means of transport measurements, and a density functional calculation. We found a giant Peltier conductivity of 100 A cm−1 K−1 at 10 K and successfully explained it by means of conventional semiconductor theory. We concluded that an uncompensated semimetal, high mobility, and heavy effective mass are responsible for the giant Peltier conductivity. Our finding opens a new ground in the field of thermoelectrics to explore much better semimetals for a new possible application such as an electric current generator for a superconducting magnet.

DOI： 10.1088/2515-7655/ac2357

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

We have measured and analyzed the in-plane thermal diffusivity of the Mott insulator Ca2RuO4 around room temperature under external currents with an infrared camera as a contactless thermometer. We find that the thermal diffusivity decreases by 40% for an external current density of 14 A=cm2. This large impact on lattice properties highly nontrivial in the sense that the external current primarily affects the electronic states. A possible explanation for this is discussed.

DOI： 10.7566/jpsj.90.063601

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

We have prepared a set of polycrystalline samples of PbPd 1 - x - y Fe y Li x O 2 (x = 0, 0.01, 0.02, 0.03, and 0.04; y = 0, 0.02, and 0.05) and have measured synchrotron x-ray diffraction and magnetization systematically. We have found high-temperature ferromagnetism in Fe- and Li-substituted samples and the largest magnetic moment of 0.023 μ B per formula unit in PbPd 0.93 Fe 0.05 Li 0.02 O 2. The ferromagnetism survives at 700 K, and the Curie temperature will be far above 800 K. Although similar but controversial high-temperature ferromagnets have been reported in many thin-film samples thus far, the discovered ferromagnetism is macroscopic in the sense that bulk samples stick to a permanent magnet at room temperature. The Fe and Li dependence of the ferromagnetism is complicated, implying that the ferromagnetism is truly unconventional.

DOI： 10.1063/5.0051283

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Science  

Bismuth silicate Bi2SiO5 (BSO) is known as an interesting new type of ferroelectric oxide; however, bulk ceramics of BSO have never been obtained because it easily decomposes at high temperature. In this study, we fabricated BSO ceramics for the first time using a sol–gel technique and investigated their potential as a dielectric material for high-temperature capacitor applications. A precursor powder was prepared by a sol–gel synthesis route using tetraethyl orthosilicate and bismuth nitrate pentahydrate as raw materials and then sintered under a small uniaxial pressure of 5 MPa with an addition of CH3COOLi as a sintering aid. A BSO ceramic with the highest relative density of 88.5% was obtained at a very low sintering temperature of 620 °C with preventing significant thermal decomposition. A crystal structure analysis revealed that the obtained BSO ceramic belongs to the ferroelectric monoclinic phase. The dielectric permittivity of the ceramic showed a superior temperature stability (± 5%) at temperatures up to 200 °C, followed by a sharp peak attributed to the ferroelectric–paraelectric phase transition at around 390 °C. The BSO ceramic also showed slim and pinched polarization hysteresis loops due to the random grain orientation and domain wall clamping, leading to a high energy storage efficiency over 75% at temperatures up to 100 °C.

DOI： 10.1007/s10853-021-05849-7

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials  

Sr8[Al12O24](SO4)2 (SAS) and Ca8[Al12O24](SO4)2 (CAS) are members of the aluminate sodalite-type oxides with the general chemical formula M 8[Al12O24](XO4)2 (M is the guest cation and XO4 is the guest anion). To discuss the role of the guest cations (M = Sr and Ca) on the rotation of AlO4 in the oxygen tetrahedral framework in the I 43m phase, the crystal structure parameters and the probability density function of the guest ions in SAS and CAS have been investigated via synchrotron radiation X-ray powder diffraction by considering Gram-Charlier expansions. The interatomic distances between the M and O ions evaluated from the maximum positions in the probability density distribution are almost equal to the sum of the ideal ionic radii of the M and O ions. This result suggests that the geometry of the AlO4 tetrahedral framework and the fluctuation of the guest ions are mainly caused by steric effects between the M and O ions.

DOI： 10.1107/S2052520621000238

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

We have measured thermoelectric properties of Ta2PdX6 (X = S, Se) around room temperature using single crystal samples. We find that the power factor of Ta2PdX6 is relatively high from middle-low to room temperatures, and notably Ta2PdSe6 shows the largest power factor among thermoelectric materials with an electrical conductivity of 10-2Ωcm at 300 K. Ta2PdS6 will be a possible candidate for a Peltier cooling material if the lattice thermal conductivity is reduced by chemical substitution.

DOI： 10.7566/JPSJ.90.033702

Web of Science

Scopus

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Open Ceramics  

The aluminum-sodalite-type oxide, Ca8[AlO2]12(MoO4)2, shows an improper ferroelectricity below a ferroelectric phase transition temperature around 630 ​K. Here we present effects of a Ga-substitution for Al on ferroelectric properties of Ca8[AlO2]12(MoO4)2. Systematic investigations with synchrotron x-ray powder diffractions and dielectric/pyroelectric measurements have clarified that the Ga-substitution suppresses the ferroelectricity and markedly enhances a thermal hysteresis of the ferroelectric phase transition. In contrast to the case of Sr-substitution for Ca, with which the ground state results in a relaxor-like state, the polar ordering of macroscopic scale has been found to survive under the Ga-substitution. The present results shed light on intuitive designing of ferroelectricity and the phase transition properties in the aluminum-sodalite-type oxide.

DOI： 10.1016/j.oceram.2021.100080

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemistry of Materials  

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 P21cn 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 Y2- 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

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics Condensed Matter  

The determination of local atomic structure at nanoscale for inhomogeneous systems is challenging. The local arrangement of atoms needs to be studied to understand the local or short-range order structures for disordered materials with a lack of long-range order periodicity. Pair distribution function (PDF) analysis is a technique, that is used to study the short-range order structure of materials: this technique is based on the evaluation of local atomic arrangement using synchrotron and neutron sources. An attempt was made to determine the local arrangement at 20 nm-scale for a typical relaxor ferroelectric material, Pb(Mg1/3Nb2/3)O3 (PMN). The PDF technique was employed owing to the limited structural coherence in this disordered material. It was determined that there are three types of structures depending on the distance. A glass-like network structure was observed as a short-range order structure owing to the large off-center shift of lead atoms. With an increase in distance, the structure of PMN changed from rhombohedral to cubic. Using the above-mentioned approach, we elucidated the process of local structure averaging.

DOI： 10.1088/1361-648x/abb866

Web of Science

Scopus

その他リンク： https://iopscience.iop.org/article/10.1088/1361-648X/abb866/pdf

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Science  

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(Mg1/3Nb2/3)O3 (PMN) and Pb(Mg1/3Nb2/3)O3–PbTiO3 (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.

DOI： 10.1007/s10853-020-05417-5

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry C  

Unusual effects of post annealing on optical and dielectric properties of (Nb0.5In0.5)0.01Ti0.99O2 (NITO-1.0%) are reported in the present study. The post-annealing performed under embedding in Al2O3 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 104, 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-TiO2 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

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of 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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本物理学会  

ファイル公開：2021-09-15

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

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

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7566/JPSJ.89.044710

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japan Society of Applied Physics  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japan Society of Applied Physics  

DOI： 10.7566/JPSJ.89.045001

Web of Science

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemistry of Materials  

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

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 電気学会  

<p>1．はじめに</p><p>私たちの身の回りでは，さまざまなエレクトロニクスデバイス素子が利用されている。例えば，抵抗器は電荷の流れを制限し，キャパシタは電荷を蓄積する。これらのデバイス素子の特性を何らかの外部刺激によってコントロールすることで，より高度なデバイス動作が得られる。抵抗器</p>

DOI： 10.1541/ieejjournal.140.28

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Inorganic Chemistry  

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

Web of Science

Scopus

PubMed

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemistry of Materials  

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

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：特定非営利活動法人 日本小児外科学会  

<p>【目的】九州小児外科研究会参加施設に臍ヘルニア治療に関する後方視的アンケート調査結果を行い，その結果に基づき臍ヘルニアのテープ固定療法の有用性を検討した．</p><p>【方法】症例登録期間は2013年1月から2015年12月までとし，2016年6月末時点での治療結果を集計した．</p><p>【結果】九州・沖縄・山口地区の24施設から回答を得た．臍ヘルニアの治癒判定はヘルニア門の閉鎖とする施設が最も多く，アンケート結果集計でもこの基準を採用した．テープ固定治療を受けた乳幼児は1,320例で，治癒と判定された症例が908例，非治癒と判定された症例は158例，皮膚障害による治療中止例が48例，転居などで中途脱落した症例が206例であった．自然経過観察症例は，テープ固定症例より大幅に少なく333例であった．治癒と判定されたのが146例，非治癒が111例，転居などで転帰不明が76例であった．治癒率はテープ固定群85.2％，自然経過群56.8％であり，テープ固定群の治癒率が有意に高かった（p＜0.05，χ2乗検定）．また治癒までの期間もテープ固定群では治癒症例の約80％の症例が治療開始から4か月以内に治癒していたのに対し，自然経過群では治癒までに1年以上かかっている症例が多かった．</p><p>【結論】臍ヘルニアのテープ固定療法は早期に治癒が得られる利点はあるが，治癒率は従来言われてきた2歳で90％という自然治癒率を超えていなかった．今回のアンケート調査による臍ヘルニアの自然治癒率は従来言われてきたものよりも低く，臍ヘルニアの自然治癒率は前向き研究による再調査が必要と思われる．</p>

DOI： 10.11164/jjsps.55.5_920

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the 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

Web of Science

Scopus

PubMed

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japan Society of Applied Physics  

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

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

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Ferroelectrics  

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

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of 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

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemistry of Materials  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of 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

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 応用物理学会  

<p>我々のグループでは最近，ゼオライトの一種であるアルミネートソーダライト型化合物において「間接型強誘電性」と呼ばれる風変わりな強誘電性を示す物質群を見いだした．アルミネートソーダライト型化合物は地球上に豊富に存在し，また主として環境親和性の高い元素によって構成されている．これまでの強誘電体材料開発はペロブスカイト型化合物を中心として進められており，キャパシタや周波数フィルタなど多くのデバイス素子として実用化に至っている．それに対して強誘電性アルミネートソーダライト型化合物は，焦電発電素子材料として鉛系ペロブスカイト型化合物も上回る特性を有し，非ペロブスカイト型強誘電体開発の新しい可能性を示している．本稿では，誘電特性や分極特性に着目しつつアルミネートソーダライト型化合物の間接型強誘電性を概説し，間接型強誘電性との関連から焦電発電素子材料としての性能を議論する．</p>

DOI： 10.11470/oubutsu.88.10_668

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.74.1.0_2549

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.74.1.0_2550

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.74.1.0_2551

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

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

Web of Science

Scopus

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：MDPI} {AG  

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

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics Condensed Matter  

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

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Materials  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of 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

Web of Science

Scopus

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.2.0_897

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_2199

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.2.0_2130

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

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

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Scientific Reports  

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

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of 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

Web of Science

Scopus

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Japanese Journal 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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of 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

Web of Science

Scopus

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Ferroelectrics  

リラクサー強誘電体Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$の局所構造解析をExtended X-ray Absorption Fine Structure (EXAFS)を用いて行った。Nb周辺の局所構造をAgNbO$_3$と比較し、Pb周辺の局所構造をPbTiO$_3$と比較した。PMNのNb周辺構造はAgNbO$_3$とよく一致しており、AgNbO$_3$と同様のNb off-center shiftに起因する1.91と2.01{\AA}の2つの結合に分裂していた。一方、disorderしたPbサイトはPDF解析から構造を抽出することに成功した。

DOI： 10.1080/00150193.2017.1350050

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Ferroelectrics  

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

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics Condensed Matter  

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

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Current Applied Physics  

DOI： 10.1016/j.cap.2017.03.013

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1111/resp.12936

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Status Solidi - Rapid Research Letters  

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

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Applied  

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

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of 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

Web of Science

Scopus

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

<p>Bi_2_SiO_5_は室温以上で強誘電性を示すシリケート化合物である。本研究ではBi_2_SiO_5_中のBiをLaで1%〜10%置換した試料を作製し、誘電率測定を行った。その結果、La置換による相転移のブロード化が観測され、置換率3％で相転移が消失した。相転移が消失した試料では100〜500 Kにわたって温度変化がほとんどない、高誘電率(ε’ 〜 100)が得られた。講演では、誘電応答の起源を格子ダイナミクスの観点から議論する予定である。</p>

DOI： 10.11316/jpsgaiyo.72.1.0_2719

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.72.2.0_2057

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics Condensed Matter  

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

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Crystals  

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

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics Condensed Matter  

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

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of 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

Web of Science

Scopus

CiNii Research

掲載種別：研究論文（学術雑誌）  

© 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

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

<p>現在, 世界的に鉛含有の物質を非鉛物質に置き換える動きが進んでいる. 人感センサなどに使用されている焦電素子では, 現在の鉛含有の物質(PZT)を凌駕する性能を示す候補物質として, 充填型ソーダライト酸化物(Ca_x_Sr_1-x_ )_8_ (Al O_2_)_12_ (WO_4_ )_2_ が提案されている. しかし, 本物質の物性については, 誘電率の温度依存性や相転移機構なども含めて未解明な点が多く残されている. そこで, 本研究では格子振動の観点からこれらの物性を理解すべく, 幅広い温度領域における広帯域顕微光散乱分光を行ったので報告する.</p>

DOI： 10.11316/jpsgaiyo.71.2.0_2553

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

<p>昨年度我々は、LaAlO_3_にZnを置換したZn:LaAlO_3_において本質的な光誘電効果を報告した。本研究では、この本質的な光誘電効果の機構を明らかにするために、窒素還元雰囲気中で焼成した還元LaAlO_3_を作製し、光照射下での誘電率測定を行った。その結果、還元LaAlO_3_でもZn:LaAlO_3_と同様の本質的な光誘電効果を観測した。講演では、大気中で焼成したLaAlO_3_での結果と合わせて、この系で観測された本質的な光誘電効果の機構について議論する。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_2514

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

<p>我々は量子スピン液体状態の可能性が指摘されているBa_3_Zn_1_Ru_2_O_9_のZnを置換したCoの磁化および磁化率測定よりこの新奇な液体状態の検証を行なっている。これまでに観測した3％置換したCoの磁化率は、キュリーもしくはキュリー・ワイス的な磁化率と明らかに異なり、40mKまでゆるやかに増加した。講演ではこれらの結果を報告し液体状態の可能性について議論する。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_1494

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.71.2.0_2587

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

<p>常磁性物質CaRuO_3_はRuに対する不純物置換により強磁性を示す。これまで我々は、非磁性元素置換効果の研究から、この強磁性がCaRuO_3_の常磁性金属相と同時に存在する強磁性クラスターグラス状態に由来することを見出した。本研究では、これらの相関を調べることを目的として、ゼーベック係数と比熱の測定を行った。講演では、クラスター形成温度近傍における伝導電子に対する磁気ゆらぎの効果を中心に議論する。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_1002

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

<p>CaPd_3_O_4_は、Pd^2+^の平面四配位構造をもつバンド絶縁体である。本研究では、PdをCuで置換した多結晶試料を作成し、Pdサイトを80%まで置換することに成功した。作成した試料について電気抵抗率、ゼーベック係数、及び磁化率の温度依存性を測定したところ、Cu置換によって基底状態がバンド絶縁体からモット絶縁体へと変化したことを示唆する結果が得られた。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_1000

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

<p>Ca_2_RuO_4_は室温付近で非線形な電気伝導現象が観測されている物質である。非線形伝導現象の観測における課題として、電流印加による自己発熱の効果がある。これまでに我々は電流通電状態でも適用可能な試料温度測定法を開発し、非線形伝導現象を捉えることに成功している。 今回はこの温度計測法を用いることで電流通電下でのゼーベック係数の測定を行った。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_1859

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of 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

Web of Science

Scopus

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nanoscale  

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

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Solid State Communications  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of 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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

DOI： 10.7567/JJAP.54.031203

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

DOI： 10.7566/JPSJ.84.014708

Web of Science

Scopus

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

Web of Science

掲載種別：研究論文（学術雑誌）  

© 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

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_2698

CiNii Books

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_2664

CiNii Books

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_2738

CiNii Books

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_2024

CiNii Books

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_2665

CiNii Books

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

DOI： 10.1063/1.4902248

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Japanese Journal of Applied Physics  

DOI： 10.7567/JJAP.53.09PB01

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Ferroelectrics  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

DOI： 10.7566/JPSJ.83.054710

Web of Science

Scopus

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

DOI： 10.1103/PhysRevB.89.195103

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Ferroelectrics  

DOI： 10.1080/00150193.2014.890470

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IUCrJ  

DOI： 10.1107/S2052252514008008

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

DOI： 10.1063/1.4872032

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Crystal Growth  

DOI： 10.1016/j.jcrysgro.2013.10.001

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

DOI： 10.1063/1.4866798

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.69.1.3.0_550_1

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.69.2.3.0_350_3

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.69.2.3.0_285_3

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.69.2.4.0_693_3

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.69.2.4.0_680_3

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4829460

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

DOI： 10.7566/JPSJ.82.104603

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

A domain structure in periodically poled stoichiometric LiNbO₃ was observed by confocal micro-Raman scanning spectroscopy. The 180&deg;-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 Nb&ndash;O bond, while there was no significant change in Li-ion related modes. Nb&ndash;O 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.

DOI： 10.2109/jcersj2.121.579

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/anie.201302188

Web of Science

Scopus

PubMed

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/pssa.201200815

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

DOI： 10.7566/JPSJ.82.074721

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Journal of Applied 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

Web of Science

Scopus

その他リンク： http://orcid.org/0000-0003-3683-5416

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0953-8984/25/13/132001

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/APEX.6.015803

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本結晶学会  

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

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.catcom.2013.04.029

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.68.2.4.0_650_3

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.68.2.3.0_583_2

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.68.1.4.0_1020_2

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.68.1.4.0_1033_2

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.68.1.3.0_581_2

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.68.1.4.0_1022_2

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.109.197601

Web of Science

Scopus

PubMed

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 応用物理学会  

<p>第一原理計算は近年大きく発展し，現実的な材料研究に広く活用される段階になっている．本稿では，この第一原理計算と高精度な実験とを連携させることにより強誘電体の相転移機構，強誘電相の構造について研究した結果を解説する．</p>

DOI： 10.11470/oubutsu.81.9_760

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jcrysgro.2012.05.030

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/c2ce25163a

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3693524

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jcrysgro.2011.12.046

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1080/00150193.2012.672035

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本結晶学会  

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

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Ferroelectrics  

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

Web of Science

Scopus

その他リンク： http://orcid.org/0000-0003-3683-5416

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

本研究では、Pulsed Laser Deposition (PLD)法によって合成したイルメナイト型MgTiO3単結晶薄膜の蛍光特性を調べた。その結果、製膜時のターゲット－基板間距離を減少させるにつれて、605nm近傍にバルク試料では見られないブロードな蛍光成分が成長することが分かった。この蛍光特性の起源を欠陥化学的観点より議論する。

DOI： 10.14853/pcersj.2012S.0.192.0

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.67.1.4.0_997_4

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.67.1.4.0_997_3

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JJAP.50.128001

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1468-6996/12/5/054204

Web of Science

Scopus

PubMed

掲載種別：研究論文（学術雑誌）   出版者・発行元：Japan Society of Applied Physics  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3643039

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/APEX.4.091501

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3609237

Web of Science

Scopus

その他リンク： http://orcid.org/0000-0003-3683-5416

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3609234

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

リラクサー(relaxor)が示す特異な誘電特性に関しては長年議論されてきたが,その本質的な発現機構は未解明のままである.本研究では,代表的なリラクサー物質であるPb(Mg_<1/3>Nb_<2/3>)O_3(PMN)を対象とし,分極測定,ラマン分光,及び透過型電子顕微鏡観察の実験結果を総合的に解析した結果,以下の結論を得た:(1)PMNにおける広範な温度領域にわたる巨大な誘電応答は分極ドメインの応答に由来する.(2)PMNは本質的にはT_c〜225Kの強誘電体である.(3)強誘電相において,ナノサイズのドメインは互いにマイクロメートルオーダーの範囲で相互作用し,全体としてより大きなドメイン構造を形成する.これらの結果より,リラクサーという複雑系物質の物理像がより明確になった.ここで明らかになった「ドメイン構造の多重スケール不均一性」とも言うべき階層的構造が,今後の巨大応答物質開発に対して新たな方向性を与えることに期待したい.

DOI： 10.11316/butsuri.66.4_270

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/jrs.2746

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3575565

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0953-8984/23/7/075901

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150193.2011.577365

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

高圧安定相であるLiNbO<SUB>3</SUB>型酸化物をPLD法で初めて作製し、その構造と物性を評価した。MnTiO<SUB>3</SUB>、FeTiO<SUB>3</SUB>ともエピタキシャル薄膜が得られ、その磁性と、強誘電性を調べた。

DOI： 10.14853/pcersj.2011F.0.626.0

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

ペロブスカイト型酸化物強誘電体CdTiO3は約８０Kで強誘電性相転移を示し、CdをCaで部分的に置換することでその強誘電性が抑制される。本研究ではCa置換による共有結合性の変化が格子振動に及ぼす効果をラマン散乱により系統的に研究し、Ca置換によるCdTiO3の強誘電性抑制のメカニズムを明らかにしたので、その結果を報告する。

DOI： 10.14853/pcersj.2011F.0.320.0

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

モルフォトロピック相境界などに代表されるように、強誘電体においては応答物性がドメイン構造や結晶構造に大きく左右されることが知られている。特に強誘電体薄膜においては基板から受ける2次元的な応力によってこれらの構造が変化するため、結晶構造やドメイン構造を積極的に制御する試みが行われている。　本研究ではパルスレーザー堆積(PLD法）によってBaTiO<SUB>3</SUB>（BTO)薄膜を基板方位の異なるSrTiO<SUB>3</SUB>（STO)上に成長させ、そのドメイン構造を圧電応答顕微鏡（PFM)によって評価したので、これを報告する。　STO(100)上に成長させたBTO薄膜は面直方向のみの分極成分がPFMによって観測され、シングルドメインとなっている。それに対してSTO(110)及び(111)上に成長させたBTO薄膜においては面直方向の分極は揃っているのに対して、面内方向の分極成分がストライプ状のドメインを構成していることが分かった。

DOI： 10.14853/pcersj.2011F.0.286.0

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.66.2.4.0_974_4

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.66.1.4.0_972_1

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.66.1.4.0_970_4

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.66.1.4.0_969_4

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.66.1.4.0_969_3

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.66.1.4.0_960_3

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/nn101036v

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.81.104105

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150191003670408

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150191003751422

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

電気分極測定、ラマン分光測定、透過型電子顕微鏡（ＴＥＭ）の観察を通して最も典型的なリラクサー材料であるPb(Mg1/3Nb2/3)O3（ＰＭＮ）を対象にしてリラクサーの挙動を系統的に調べた。その結果、(1)通常ＰＭＮで270K付近に観測された巨大な誘電応答は分極反転に由来することが判明した。(2)PMNがＴ＜Ｔc=225以下で多重ドメイン構造を示す強誘電体であることが分かった。

DOI： 10.14853/pcersj.2010S.0.3A20.0

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.1.4.0_976_3

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.2.4.0_916_1

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.2.4.0_903_4

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.2.4.0_902_2

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.2.4.0_900_2

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.2.4.0_891_1

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.1.4.0_998_3

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.1.4.0_985_2

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.1.4.0_985_1

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.1.4.0_984_4

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3275750

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.103.207601

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/cm802483w

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150190902852117

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

BiFeO3は高い自発分極値や室温において強誘電性と反強磁性を有する物質として近年大きな注目を集め非常に多くの研究がなされている。しかしながら強誘電相転移点が820&ordm;C付近と非常に高温であることとさらに物質自体の不安定性もあり、BiFeO3の相転移挙動についてはいまだによくわかっていない。そこで本研究ではBiFeO3単結晶をflux法によって作成したサンプルについてラマン散乱を行った。サンプルは分極軸に垂直な(110)hex面に切り出したものを用いた。ラマンスペクトルの回転依存性及び偏光依存性を調べることによってA1モードとEモードを分離することができた。

DOI： 10.14853/pcersj.2009F.0.1PA34.0

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/pssr.200903090

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

LiNbO3（Lithium Niobate: LN）は、表面弾性波デバイスおよび非線形光学素子として広く使用されている材料であり、これまで多くの研究がなされている。今回、いくつかのRaman散乱ピーク強度の組成依存性を測定し、LN結晶欠陥との関連を調べた。組成およびMg添加量の異なる４種類のLNについて、バックスキャッター配置でラマン測定を行った。その結果、いくつかの散乱ピークに著しい組成依存性を窺うことができた。これらのピークに対し、いくつかの仮定の下で理論解析を行い、欠陥量の相対比較をおこなった。その結果、それぞれのピークがLNの欠陥（Ndアンチサイト欠陥・Li空孔）に関連していると考えると、上述した組成依存性は欠陥平衡モデルに照らし合わせ矛盾なく説明できる。

DOI： 10.14853/pcersj.2009S.0.166.0

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

独自に開発した精密共焦点顕微分光システムを用いて、LiNbO₃単結晶におけるアンチパラレルドメイン構造の観測を行った。従来、アンチパラレルドメインはラマン選択則の等価性の為にラマン分光法では観測不可能と考えられてきた。それに対して本研究では、ドメイン境界に生じる微小な格子歪みを高精度で検出することにより、LiNbO₃のアンチパラレルドメインを500nm以下の空間分解能で正確に観測することに成功した。本研究の結果は、非接触・非破壊・非侵襲による革新的なドメインイメージング技術を新たに開拓するものである。さらに、詳細なスペクトル解析によってドメイン境界に生じる格子歪みの原因も明らかにしたので、この結果も合わせて報告する。

DOI： 10.14853/pcersj.2009F.0.1G20.0

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.64.2.4.0_885_4

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.64.1.4.0_984_3

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.64.1.4.0_951_3

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.64.2.4.0_680_2

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.64.2.4.0_887_2

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.64.2.4.0_886_3

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.78.172103

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/cm801905d

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/cm0710507

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.mseb.2007.09.030

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150190802371242

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.63.1.4.0_944_2

CiNii Research

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150190802365962

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.2918837

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150190802377918

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.77.224104

Web of Science

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

ペロブスカイト型構造を有するCdTiO<SUB>3</SUB>は室温ではTiO6八面体が回転したPnma構造をとり，約85Kにおいて強誘電体に転移することが報告されているが，その強誘電相の構造などはこれまで詳細な解析はなされていなかった．本研究では，第一原理計算によるフォノン分散の計算を行い，Pnma相におけるソフトモードの存在，また，そのソフトモードから導かれる低対称性相について検討を行った．

DOI： 10.14853/pcersj.2008F.0.184.0

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.63.2.4.0_870_4

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.63.2.4.0_884_2

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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.

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.99.017602

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150190701515790

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.62.2.4.0_996_1

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.2751136

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150190601187500

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

Pb系ABO<SUB>3<SUB>型酸化物が優れた圧電性や強誘電性を有するのはA-site元素である鉛と酸素の強い結合性によって生じる原子変位に深く関係すると報告されている。それは非鉛系新規材料の探索に良い指針を与えてくれる。われわれはAg系酸化物に52uC/cm2以上極めて大きな分極が存在することを発見した。その巨大な分極がA-siteのAgとOの結合に由来すると提案している。その発見は新規強誘電体の開発に新たな道を開くことを強く期待している。

DOI： 10.14853/pcersj.2007F.0.503.0

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/430_2006_046

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1080/00150190600738196

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/cm0525555

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/BF02679539

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JJAP.45.152

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日露/CIS/バルチック強誘電体シンポジウム組織委員会  

DOI： 10.11533/rcbjsf.2006.0.42.0

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本セラミックス協会  

無容器法によって作製されたBaTi<SUB>2</SUB>O<SUB>5</SUB>ガラスは、強誘電体を基にしてガラス形成物質の添加無しに作られた初めてのバルクガラスであり、新ガラス材料として極めて多くの注目を集めている。この物質は結晶化過程において10<SUP>7</SUP>にも及ぶ巨大な誘電異常を示すがその起源は明らかになっておらず、結晶化過程の解明が強く望まれている。本研究ではラマン散乱を用いてBaTi<SUB>2</SUB>O<SUB>5</SUB>ガラス結晶化過程のその場観察を行なった。その結果、α相とβ相の２つの準安定ナノ結晶相の生成を伴った段階的な結晶化過程を明らかにした。さらに巨大な誘電異常がα相に起因することを解明した。

DOI： 10.14853/pcersj.2006F.0.19.0

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日露/CIS/バルチック強誘電体シンポジウム組織委員会  

DOI： 10.11533/rcbjsf.2006.0.3.0

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日露/CIS/バルチック強誘電体シンポジウム組織委員会  

DOI： 10.11533/rcbjsf.2006.0.80.0

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

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

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.60.2.4.0_803_2

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.60.1.4.0_890_4

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.60.1.4.0_913_3

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人日本物理学会  

The ferroelectric microregion (FMR) in quantum paraelectric SrTiO<SUB>3</SUB> is studied by Raman scattering using an optical cryostat with a <SUP>3</SUP>He refrigerator. By the partial exchange of the oxygen atom for its isotope <SUP>18</SUP>O, 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 <SUP>18</SUP>O.

DOI： 10.1143/JPSJ.73.3262

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：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.

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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<SUB>3</SUB><SUP>2&minus;</SUP> anions through two different types of hydrogen bonds with the bond angles of 179.2 and 171.6&deg;. Two independent deuterons within the hydrogen bonds forming the chains are disordered over two sites separated by 0.545 and 0.539 &Aring;. 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&ndash;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&deg; 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&deg; 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.

DOI： 10.1143/JPSJ.73.107

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.59.2.4.0_867_2

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

Crystal structure of H<SUB>3</SUB>NCH<SUB>2</SUB>COOH&middot;H<SUB>2</SUB>PO<SUB>3</SUB> 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(HPO<SUB>3</SUB>)<SUP>&minus;</SUP> chains are disordered over two sites with the separations of 0.486(3) and 0.474(5) &Aring; 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&ndash;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 HPO<SUB>3</SUB><SUP>2&minus;</SUP> anions in the F phase.

DOI： 10.1143/JPSJ.72.1111

Web of Science

Scopus

CiNii Research

担当ページ：-   記述言語：日本語 著書種別：学術書

記述言語：英語 著書種別：学術書