Authorship：Lead author,　Corresponding author   Language：English   Publisher：The Ceramic Society of Japan  

<p>We have prepared a dense ceramic sample of a novel thermoelectric sulfide Ta₂PdS₆ by means of spark plasma sintering technique under a uniaxial pressure. The Rietveld analyses of the X-ray diffraction patterns have clarified occurrence of weak preferred orientation in the sintering process. Resistivity, thermopower, and Hall resistivity measurements on the ceramic sample have indicated that it shows higher carrier density and lower carrier mobility than a single crystal. The inferior carrier mobility in the ceramic sample may partly come from increased point-defect and/or grain-boundary scattering, to which poor power factor is attributed.</p>

DOI： 10.2109/jcersj2.23038

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CiNii Research

Authorship：Lead author,　Corresponding author   Language：English   Publisher：Journal of Materials Chemistry C  

We have investigated the physical properties of an oxygen-deficient perovskite-type Sr10Ga6Sc4O25 by means of dielectric permittivity, pyroelectric current, and X-ray diffraction (XRD) measurements using a polycrystalline sample. The real part of the dielectric permittivity shows a clear anomaly around 310 K. Switchable pyroelectric current is also observed around this temperature, indicating a ferroelectric phase transition in the title compound. Synchrotron powder XRD measurements reveal that no discontinuous jump takes place in the temperature dependent cell volume around 310 K, implying that the phase transition is of second order. The candidates of the low and high temperature space groups are discussed based on the group theory.

DOI： 10.1039/d2tc05118d

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

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

DOI： 10.7566/JPSJ.91.023701

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Publisher：Journal of the Physical Society of Japan  

We have prepared a set of polycrystalline samples of Ba3Ca(Ru1−xNbx)2O9 consisting of the face-shared (Ru,Nb)2O9 dimer block from x = 0 to 0.12, and have measured the x-ray diffraction and magnetization. We find that all the samples of x > 0 show Curie–Weiss-like susceptibility below 30 K with the Weiss temperature θNb of 2–7 K, which suggests that the Nb-substituted NbRuO9 dimer interacts the Ru2O9 dimers magnetically. We also find the NbRuO9 dimer effectively works as S = 1 in the dilution limit, which is also suggested by the first-principle calculation. The Ru2O9 dimer lattice is nontrivial in the sense that S = 1 moment in the NbRuO9 dimer is screened for large x without any magnetic long range order. A possible origin is discussed.

DOI： 10.7566/JPSJ.90.114706

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

DOI： 10.1039/d1tc03897d

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

DOI： 10.1063/5.0051283

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Authorship：Lead author,　Corresponding author   Language：English   Publisher：Physical Society of Japan  

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本物理学会  

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

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.1.0_2550

CiNii Research

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.1.0_2549

CiNii Research

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.1.0_2551

CiNii Research

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

DOI： 10.1103/PhysRevB.98.045139

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

DOI： 10.1107/S2052252517018334

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Language：English   Publisher：ACS Nano  

Domains in a crystal, which have crystallographic uniformity and are geometrically segmented, typically arise from various phase transitions. The physical properties within individual domains are inherently the same as those in the homogeneous bulk. As a result, sufficiently large domains have little influence on the bulk properties. However, as the domains decrease in size to the nanoscale, for instance, due to multiple phase instabilities or spatial inhomogeneities, then the materials often acquire exceptional functionalities that are unattainable without these domains. This effect is exemplified by the ultrahigh dielectric and piezoelectric responses observed in ferroelectric oxides with nanoscale polar domains as well as in ferroelectric relaxors with polar nanoclusters. Here, we demonstrate that hashed nanoscale domains in an antiferroelectric material are also capable of boosting dielectric permittivity in an unconventional way. This discovery has been made in an antiferroelectric titanite-type oxide, CaTi(Si1-xGex)O5, in which the permittivity significantly increases when the antiferroelectric order becomes short-range. Our transmission electron microscopy observations have clarified that polar regions simultaneously appear around antiphase boundaries in the antiferroelectric phase of CaTi(Si1-xGex)O5. As the concentration of the antiphase boundary increases, the polar regions become denser and play a crucial role in boosting the permittivity. At the composition of x = 0.5, the value of the permittivity finally reaches double that in the bulk and shows excellent linearity, at least until an electric field of 500 kV/cm is applied. The present findings highlight the promise of domain engineering for boosting the permittivity in antiferroelectrics as a way to develop materials with excellent dielectric properties.

DOI： 10.1021/acsnano.4c02168

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/PhysRevB.109.L100101

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.109.L100101/fulltext

Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsaelm.3c01129

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society ({APS})  

DOI： 10.1103/PhysRevMaterials.6.044412

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

DOI： 10.7566/JPSJ.90.074706

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

DOI： 10.7566/JPSJ.90.063601

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

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chemistry of Materials  

DOI： 10.1021/acs.chemmater.0c04032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Materials Chemistry C  

DOI： 10.1039/d0tc03539d

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

DOI： 10.7566/JPSJ.89.093707

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Language：English   Publisher：Physical Review B  

DOI： 10.1103/PhysRevB.101.094108

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

DOI： 10.1021/acs.chemmater.9b04022

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Publisher：The Japan Society of Vacuum and Surface Science  

<p>Ta₂NiSe₅ is a candidate for the excitonic insulator. Recent photoemission study revealed that the valence band minimum shifts to the low energy side at low temperature, which is consistent with the excitonic insulator. To confirm this, it is necessary to observe the conduction band. In this study, we examined the conduction band of Ta₂NiSe₅ using the low energy inverse photoelectron spectroscopy (LEIPS). The lowest unoccupied band was observed at 0.55 eV above the Fermi level. This band did not shift at the low temperature of 80 K. This result supports the recent proposed picture that the Ta₂NiSe₅ is different from the conventional excitonic insulator; the noninteracting band structure is a band-overlap semimetal and the bandgap opens by the strong electron-hole attraction.</p>

DOI： 10.14886/jvss.2020.0_135

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

DOI： 10.1021/acs.chemmater.9b02373

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

DOI： 10.1103/PhysRevB.99.104109

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

DOI： 10.1039/c7cc08202a

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

DOI： 10.1021/acsami.7b14132

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