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

DOI： 10.1088/1361-648x/ac0dd7

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

DOI： 10.1103/physrevb.103.224408

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.103.224408/fulltext

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

A SnI4 molecule lowers its symmetry from T-d to C-3v on the liquid-liquid transition. Because it is possible to lower the molecular symmetry without violating the crystalline symmetry, it is worth examining whether the deformation occurs in the crystalline phase field. Extended x-ray absorption fine structure (EXAFS) measurements on the crystalline state were carried out to investigate the change in the environment around a Sn atom at high pressures and temperatures. We could not find clear evidence on the symmetry change of molecules even close to the melting points, where the melting curve becomes abnormally flat against pressure. Indeed, no inconsistency was found when we assumed that the coordination number of a Sn atom remains unchanged in the temperature and pressure range examined. The situation remains true when the system entered the high-pressure crystalline phase on compression. We can propose a consistent scenario as to the structural change on the phase transformation. The incompressibility of a SnI4 molecule could be suitably quantified. The procedure enabled us to conclude the molecule is more than an order of magnitude incompressible than the lattice.

DOI： 10.1088/1361-648x/ab4cbc

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

DOI： 10.1088/1361-648x/ab49b5

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

Cu0.25Bi2(TexSe1-x)3 is a material in which tellurium atoms (Te) partially occupy selenium (Se) sites in a crystal structure of the superconductor Cu0.25Bi2Se3. This study focuses on the composition of x = 0.01, Cu0.25Bi2(Te0.01Se0.99)3, and we performed electrical resistivity measurement and X-ray diffraction under high pressures. Cu0.25Bi2(Te0.01Se0.99)3 shows slight diamagnetism and a drop in resistivity at ambient pressure
this suggests possible superconductivity at the transition temperature of Tc = 3.2 K, which is suppressed at P = 1 GPa. On further compression, a slight drop in resistivity is observed at temperatures of 4.3-5.4 K above 10 GPa. This drop is suppressed under magnetic fields, suggesting the occurrence of superconducting transition. The pressure-induced structural phase transition from a trigonal R3m phase to a sevenfold monoclinic C2/m phase occurs at 10.9 GPa. These results suggest that the superconducting transition above 10 GPa occurs in the high-pressure C2/m phase.

DOI： 10.7567/JJAP.56.05FB04

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

We performed x-ray diffraction and electrical resistivity measurement up to pressures of 5 GPa and the first-principles calculations utilizing experimental structural parameters to investigate the pressure-induced topological phase transition in BiTeBr having a noncentrosymmetric layered structure (space group P3m1). The P3m1 structure remains stable up to pressures of 5 GPa; the ratio of lattice constants c/a has a minimum at pressures of 2.5-3 GPa. In the same range, the temperature dependence of resistivity changes frommetallic to semiconducting at 3 GPa and has a plateau region between 50 and 150 K in the semiconducting state. Meanwhile, the pressure variation of band structure shows that the bulk band-gap energy closes at 2.9 GPa and re-opens at higher pressures. Furthermore, according to the Wilson loop analysis, the topological nature of electronic states in noncentrosymmetric BiTeBr at 0 and 5 GPa are explicitly revealed to be trivial and nontrivial, respectively. These results strongly suggest that pressure-induced topological phase transition in BiTeBr occurs at the pressures of 2.9 GPa.

DOI： 10.1103/PhysRevB.95.125203

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_2227

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_2233

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_1850

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

We present a method for determining the number of stacked layers in graphene by exploiting its light-shielding effect. If a substrate supporting graphene has Raman-active modes, its Raman bands can be obtained simultaneously with the G and G' bands of graphene. The Raman intensities from the substrate decrease with increasing the number of graphene layers because of the low opacity of graphene for visible light. The relationship between the number of graphene layers n and the relative intensities I-n,I-h/I-0,I-h from the substrate can be represented by I-n,I-h/I-0,I-h = 0.977(2n), on the basis of the optical transmittance of visible light for single-layer graphene. The method is simple, convenient, highly accurate, and can be used to count beyond six layers up to 30 layers. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4937140

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

The crystal structure and electrical resistivity of YBa2Cu4O8 (Y124) were studied under high pressure up to 18 GPa using diamond-anvil cells, respectively, in order to clarify its conduction mechanism. Y124 causes the first-order phase-transition into the orthorhombic Immm at pressure around 11 GPa. The high-pressure phase (HPP) also shows the superconductivity, while the manner of temperature dependence of electrical resistance and the pressure dependence of transition temperature, T-c, drastically change above 11 GPa. The CuO2 plane persists in HPP but the CuO double chains collapse with the phase transition and transform into three-dimensional Cu-O network, resulting in the renewal of conduction system.

DOI： 10.7566/JPSJ.83.093601

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Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing  

We performed x-ray diffraction study and electrical resistivity measurement of non-stoichiometric n-type Bi35Te65 under high pressure to investigate pressure-induced superconductivity and structural phase transition. Stoichiometric bismuth telluride (Bi2Te3), which is a p-type semiconductor, has the rhombohedral structure with space group R-3m at ambient condition. Pressure-induced superconductivity of stoichiometric p-type Bi2Te3 occurs in the high-pressure phases which appear above 8 GPa. Bi35Te65 has also the R-3m structure at ambient condition with electron carriers. X-ray diffraction study shows that the R-3m structure remains stable up to 8 GPa at room temperature. The superconducting transition in n-type Bi35Te65 is observed above 6 GPa; the transition temperature is 2.9 K at 6 GPa. The electrical resistivity at room temperature decreases rapidly at pressures from 7 to 8 GPa, indicating the occurrence of structural phase transition. It suggests that the superconducting transition at 6 GPa occurs at the ambient pressure phase with the R-3m structure. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/500/19/192003

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

DOI： 10.7566/JPSJ.82.045002

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Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

DOI： 10.4131/jshpreview.23.354

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We have performed powder x-ray diffraction study on BaFe2As 2 under hydrostatic pressures up to 6 GPa at room temperature. Hydrostatic pressure was produced by means of a diamond anvil cell with He gas as a pressure transmitting medium. Single crystalline sample of BaFe 2As2 was ground in alumina mortar cooled with liquid nitrogen to produce a fine powder sample. The diffraction patterns show a tetragonal structure with a space group of I4/mmm in the whole pressure range. Rietveld analysis on the experimental results shows that the lattice parameters are monotonically decreased with increasing pressure. The As-Fe-As bond angle does not reach the ideal tetrahedral value of 109.47°. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/400/2/022017

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Pressure variation of the electrical and structural properties of bismuth-antimony alloy at the composition of x = 0.15 (Bi0.85Sb 0.15) has been studied by electrical resistivity and synchrotron radiation x-ray diffraction measurements up to 10 GPa. The crystal structure changes from the A7 structure to the incommensurate host-guest composite one at 3 GPa and room temperature. Temperature dependence of the resistivity greatly changes from the semiconducting behaviour to the metallic one associated with the structural phase transition. Pressure-induced superconducting transition of Bi0.85Sb0.15 is observed above 4.5 GPa. The transition temperature Tc is found to decrease from 6.79 GPa at 4.5 GPa to 5.82 K at 9.5 GPa with increasing pressure. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/400/2/022088

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

Electrical resistivity and x-ray diffraction measurements have been carried out to investigate the pressure effect on the critical temperature for superconductivity (T-C) and lattice parameters ofAlB(2)-type superconducting silicide YbGa1.1Si0.9 (T-C = 2.4 K) and its referencematerial CaGaSi (T-C = 4.5 K). The electrical resistivity measurements up to 2.5 GPa reveal that T-C decreases with pressure for both silicides and the pressure derivative of T-C (dT(C)/dP) is -0.78 K/GPa and -0.026 K/GPa for YbGa1.1Si0.9 and CaGaSi, respectively. X-ray diffraction measurements up to 3.5 GPa indicate both silicides do not exhibit structural changes in this pressure range and they have similar values for the bulk moduli: B-0 = 40 +/- 2 GPa for YbGa1.1Si0.9 and B-0 = 42 +/- 1 GPa for CaGaSi. The relative pressure derivative of T-C (dlnT(C)/dP) and logarithmic volume derivative of T-C (dlnT(C)/dlnV) are -0.33 GPa(-1) and 13 in YbGa1.1Si0.9. These values are about tenfold larger than those for other AlB2-type superconductors. Additionally, the origin of dlnT(C)/dP and dlnT(C)/dlnV in YbGa1.1Si0.9 relative to the pressure effect on the valence of Yb atoms is discussed.

DOI： 10.1103/PhysRevB.84.104520

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Raman, IR, and visible absorption spectra of scandium trihydride (ScH3) have been measured at high pressures up to 50 GPa, to investigate the structural and electronic phase transitions. Successive hcp-intermediate-fcc phase transitions were observed at 25 and 46 GPa by Raman and IR measurements. It was suggested that the intermediate phase of ScH3 takes the same structure as that of YH3 with a long periodicity of the stacking of the metal planes. The visible absorption spectra allowed us to determine that the energy gap of ScH3 is 1.7 eV at the ambient condition and is closed around 50 GPa, at which the crystal structure transforms to fcc.

DOI： 10.1103/PhysRevB.84.064132

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DOI： 10.1103/PhysRevB.83.092102

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

The compressibility of lanthanum (La) metal and its hydrides were measured at room temperature by high pressure synchrotron X-ray diffraction. La metal pressurized in a hydrogen medium forms a hydride with an fcc metal lattice, which likely contains hydrogen at a concentration close to 3.0 and persists over the measured pressure span up to 21 GPa. Equations of state have been determined by helium compression experiments for LaH2 with tetrahedral interstitial sites fully occupied with hydrogen atoms and for LaH2.46 with octahedral interstitial sites partially occupied with hydrogen atoms and tetrahedral sites fully occupied. Both hydrides possess fcc metal lattices. The bulk modulus values B-0 are 66.7 +/- 1.2 GPa for LaH2 and 68.4 +/- 1.0 GPa for LaH2.46. These values are three times larger than that of La metal and are very close to each other despite the difference in hydrogen occupation states. The hardening of the metal lattice by hydrogenation is attributed predominantly to hydrogen-metal interactions at the tetrahedral sites and is most pronounced for La, which has the largest ionic radius among rare-earth metals. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2010.12.030

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Pressure evolution of structural and electrical properties of boron triiodide, a highly anisotropic molecular crystal consisting of stacked layers of planar BI3 molecules, has been studied by x-ray diffraction and resistivity measurements. A new phase transition was observed to occur at 6.2 GPa from the molecular phase with hexagonal structure to a monatomic phase with the face-centered-cubic lattice of iodine atoms. This first-order phase transition is characterized by the discontinuous crush of stacking of molecular layers. The monatomic phase becomes metallic at ∼23?GPa and exhibits superconductivity above ∼27?GPa. The process of molecular dissociation and electrical properties of BI3 are discussed in comparison with those of iodine and other simple molecular iodides. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevB.82.094506

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Powder x-ray diffraction experiments have been done on Ne up to 237 GPa at room temperature. Ne remains in the fcc phase up to the highest pressure. In order to observe the weak 200 reflection at ultrahigh pressures, we have used the tube-cross slit at the exit side of x-rays, which effectively reduced the scattered x-rays by the diamond anvil. The lattice parameters obtained from the 111 and 200 reflections significantly differ from each other, implying the existence of sizable uniaxial stress in Ne at ultrahigh pressures. On the basis of the calculated elastic constants of Ne at high pressures, we conclude that the 111 reflection is least affected by the uniaxial stress. The equation of state constructed from the 111 reflection agrees well with previous data. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/215/1/012017

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Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing  

We have investigated the pressure dependence of superconducting transition temperature Tc of Bi2Te3 through electrical resistance measurement under high pressure up to 13 GPa. The value of zero-resistance critical-temperature Tczero is 2.7 K at 9.0 GPa. Pressurization up to 11 GPa reduces the Tczero. However the pressurization at 13 GPa causes sudden enhancement of T czero, which is obtained to be 3.7 K. The onset temperature of superconducting transition Tconset shows the positive pressure dependence under pressure above 10 GPa. The value of Tconset is obtained to be 5.0 K at 13 GPa. The sharp increase of Tczero and the positive pressure dependence of Tconset suggest a presence of new superconducting phase. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/215/1/012036

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DOI： 10.1088/1742-6596/215/1/012047

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

We succeeded in synthesizing Ba2RBiO6 (R = La, Ce, Nd, Sm, Eu, Gd, and Dy) with a double-perovskite structure. Its photocatalytic activities were then investigated for a degradation of methylene blue (MB) solution and gaseous 2-propanol (IPA). High photocatalytic activities were observed under visible light irradiation and also a rare earth dependence of photocatalytic activities in the IPA degradation. We carried out first-principle calculations of the band structure based on the all-electron Full-potential Linear Augmented Plane-Wave (FLAPW) method and discuss the relationship between the high photocatalytic activities and the band structure in this paper. (C) 2010 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.118.91

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

Pressure dependence of the superconducting transition temperature T-c has been investigated in YbGa1.1Si0.9, which is the AlB2-type layered superconductor with T-c = 2.4 K. The electrical resistivity measurements were carried out under hydrostatic pressure up to 2.5 GPa using a piston-cylinder type pressure cell. With increasing pressure, the T-c of YbGa1.1Si0.9 decreases from 2.4 K to 1.1 K at 2.5 GPa with a pressure derivative of T-c, dT(c)/dP, of -0.78 K/GPa. This negative pressure derivative of T-c is similar to the other superconducting AlB2-type silicides. The relative pressure derivative of T-c, dlnT(c)/dP, for YbGa1.1Si0.9 is - 0.33 GPa(-1), which is about ten times larger than those for other layered superconductors.

DOI： 10.1088/1742-6596/215/1/012035

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The structure of pressure-induced amorphous form of SnI4 has been studied by synchrotron x-ray diffraction measurements using diamond-anvil cell. The structure factor, the reduced radial distribution function, and the density were obtained between 25 and 55 GPa. Comparison of measured structure factor with that calculated for a randomly oriented dimerized molecules model shows no similarity between them. Experimentally obtained radial distribution function provides clear evidence for the absence of both distances between tin and iodine atoms and between iodine atoms within the SnI4 tetrahedral molecule. Characteristic features of the structure factor for amorphous SnI4 show a marked resemblance to those for elemental metallic glasses which are successfully reproduced by a model of dense random packing of equal-sized spheres. Indeed, various quantities such as positions of peaks in measured structure factors and in experimental radial distribution functions, the coordination number are in precise agreement with those derived from the dense random-packing model. We conclude that the structure of the high-pressure amorphous form of SnI4 is the relatively rigid packing of tetrahedra composed of iodine and substitutional tin atoms. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevB.80.054201

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

The structure of pressure-induced amorphous form of SnI4 has been studied by synchrotron x-ray diffraction measurements using diamond-anvil cell. The structure factor, the reduced radial distribution function, and the density were obtained between 25 and 55 GPa. Comparison of measured structure factor with that calculated for a randomly oriented dimerized molecules model shows no similarity between them. Experimentally obtained radial distribution function provides clear evidence for the absence of both distances between tin and iodine atoms and between iodine atoms within the SnI4 tetrahedral molecule. Characteristic features of the structure factor for amorphous SnI4 show a marked resemblance to those for elemental metallic glasses which are successfully reproduced by a model of dense random packing of equal-sized spheres. Indeed, various quantities such as positions of peaks in measured structure factors and in experimental radial distribution functions, the coordination number are in precise agreement with those derived from the dense random-packing model. We conclude that the structure of the high-pressure amorphous form of SnI4 is the relatively rigid packing of tetrahedra composed of iodine and substitutional tin atoms.

DOI： 10.1103/PhysRevB.80.054201

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A single-crystalline sample of BaFe2As2 was prepared by high-pressure synthesis, and temperature dependence of resistivity was measured under high pressures of up to 9.0 GPa. Application of 3.0 GPa pressure suppresses the spin-density wave transition and induces superconductivity with the zero resistance state at a superconducting transition temperature T-c=35 K. T-c decreases monotonically with increasing pressure. The appearance of the superconductivity and the disappearance of the anomaly due to the spin-density wave transition occur simultaneously at a pressure of 3.0 GPa. At 3.0 GPa, a superconducting transition is induced in BaFe2As2; however, the superconductivity is suppressed at higher pressure.

DOI： 10.1103/PhysRevB.79.172506

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Raman and visible absorption study were performed for YH3 and ScH3 at high pressures, in order to clarify the structural and electronic phase transitions. The Raman results of YH3 revealed the presence of an intermediate phase at 9-24 GPa between the low-pressure hexagonal and high-pressure fcc phases. The characteristic behaviour was commonly observed for vibrational properties of YH3 and ScH3, suggesting a common mechanism of the structural transformation. The results of the absorption measurements for YH3 demonstrate that the optical band gap starts to close in response to the phase transition. © 2008 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/121/4/042011

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

Transparent orange yttrium hydride turns to black when illuminated by visible laser light at pressures of several gigapascals at room temperature. The marked reduction in optical transmittance extends over the infrared region, suggesting that illumination creates persistent free carriers. The opaque black sample returns to the transparent orange hydride during room-temperature annealing for a few hours. Photochromism is pronounced for the coexistent state of the metallic fcc-YH2 and the insulating hexagonal-YH3 state but is depressed for the single phase of hexagonal-YH3. The results indicate that light illumination can modify the optical and possibly electronic properties during a certain period of times.

DOI： 10.1063/1.2794755

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Raman and visible absorption spectra of YH3 were measured at high pressures, in order to clarify the structural and electronic phase transitions. The Raman results revealed the presence of an intermediate phase at 9-24 GPa between the low-pressure hexagonal and high-pressure fcc phases. The Y-framework structure and the position of interstitial H atoms are changed on the transition to intermediate phase. The results of the absorption measurements demonstrate that the optical band gap starts to close in response to the phase transition.

DOI： 10.1103/PhysRevB.76.024107

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We constructed a single-crystal synchrotron X-ray diffraction system to precisely study the structure under hydrostatic pressure conditions at low temperatures and applied it to a study on the phase transition phenomena of a Cd-Yb periodic approximant and a Cd-Yb quasicrystal. Four phases were newly observed for the 1/1 approximant crystal in a P-T range up to 5.2 GPa and down to 10 K. The innermost part of the atomic clusters of Cd4 tetrahedra exhibited various orientational ordering sensitively depending on pressure and temperature. High pressure diffraction measurements using a highly parallel synchrotron X-ray beam and a hydrostatically compressed single crystal enabled us to detect the weak diffractions due to the subtle structural changes.

DOI： 10.1080/14786430701358707

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Pressure induced structural transition of yttrium hydride has been investigated using synchrotron radiation X-ray diffraction measurement up to 24 GPa at room temperature. A reversible hexagonal-fcc transition with a wide intermediate region from 11 to 20 GPa is confirmed, which is consistent with previously reported X-ray results. The diffraction patterns measured for the intermediate state are not interpreted in terms of a hexagonal-fcc coexisting state or as rare-earth structures with various metal-layer stacking sequences. The equation of state determined for the hexagonal-YH3 provides a bulk modulus B0 of 71.9 GPa, which is nearly half of the previously reported value, but is within the range of values reported for other rare-earth metal trihydrides with hexagonal structures. © 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2006.04.011

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

Synchrotron radiation x-ray diffraction experiments on the pressure-induced ferromagnetic superconductor UGe2 has been performed using a diamond anvil cell (DAC)diffractometer to study the correlation between the crystal structure and ferromagnetism. The oscillation photos covering the three-dimensional reciprocal spaces were taken both below and above a critical I entperai uni T-x at pressures up to 1.1 GFa. Coupled charge density wave (CDW) tnul spin density wave (SDW) fluctuations were predicted as an origin of unusual properties of UGe2 by Watanabe and Miyake, but no additional superlttice Bragg peaks corresponding to the CDW reflections could be observed, resulting in an upper limit of its intensity of similar to 1 x 10(-4) to the fundamental Bragg peak intensity.

DOI： 10.1143/JPSJS.75S.88

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High prebure infrared spectra were measured for yttrium trihydride, YH3, prepared by hydrogenation of yttrium metal in hydrogen fluid at prebures around 1 GPa. The spectral change with an hcp-fcc structural transition was observed at about 10 GPa in agreement with X-ray diffraction results. With further increase in prebure to 23 GPa, the hydride became opaque suddenly in the whole infrared region. X-ray diffraction measurement showed that the metal lattice maintained the fcc structure acrob the electronic transition likely with band gap closure. The 1s metal theoretically predicted was probably realized in YH3 at high prebures.

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Using in situ x-ray diffraction measurements, the location of the liquidus in low-pressure crystalline-liquid phase boundary of Snl4 was investigated. The liquidus of low pressure crystalline phase of SnI4 was determined up to approximately 3.5 GPa. It was found that the liquidus is not well fitted to a monotonically increasing curve such as Simon's equation, but breaks near 1.5 GPa and then becomes flat. It was also found that the liquidus breaks near 1.5 GPa and becomes rather flat in the higher-pressure regime.

DOI： 10.1063/1.1751397

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We have performed a high-pressure synchrotron x-ray diffraction study of a metallic amorphous state in SnI4 induced by pressure. The Faber-Ziman structure factor S(Q) was obtained from diffraction intensities measured at pressures between 25 and 65 GPa. The first peak in S(Q) is relatively intense and sharp and the second peak is overlapped with the third one. Such features are also found in S(Q) for pure metallic glasses of Ni and Fe at 1 atm but not in molecular liquids. The obtained reduced radial distribution function g(r) shows no evidence for the presence of the SnI4 molecules in the metallic amorphous state.

DOI： 10.1088/0953-8984/14/44/331

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The polar semiconductor BiTeBr has the P3m1 symmetry, similar to that of BiTeI, in which a pressure-induced topological phase transition from a trivial semiconductor to a topological insulator has been theoretically predicted. To investigate the topological phase transition in BiTeBr, we performed X-ray diffraction and electrical resistivity measurement under high pressure, and the band calculation using experimental structural parameters. The P3m1 structure is stable up to the pressure of similar to 7 GPa; the ratio of lattice constants (c/a) reaches a minimum at around 3 GPa. Furthermore, the following phenomena are observed at around this pressure; 1) the band-gap energy closes and reopens with pressure, 2) the temperature dependence of resistivity changes from metallic to semiconducting. From theoretical prediction in BiTeI, the topological phase transition is accompanied by the band gap closing/reopening. Therefore, the results obtained in BiTeBr suggest that the topological phase transition occurs at around 3 GPa.

DOI： 10.1088/1742-6596/950/4/042036

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：The Japan Society of High Pressure Science and Technology  

Energy-related materials are expected to reinforce energy security and solve worldwide environmental problems. We are currently focusing on the developments of advanced hydrogen storage materials for fuel cell technologies. Actually we have studied new metal-, complex- and perovskite-hydrides composed of light elements using high pressure technique and microwave process. In addition, hydrides researches connected with secondary battery and neutron shield have being also progressed, aiming at searching new functional materials. In this article, we introduce our recent studies of various hydrides for energy-related applications.

DOI： 10.4131/jshpreview.18.180

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Other Link： https://jlc.jst.go.jp/DN/JALC/00314062299?from=CiNii

Language：Japanese   Publishing type：Book review, literature introduction, etc.  

The highly compressed state of metal hydride has been investigated to explore structural and electronic transitions characteristic to hydride. The hydrogen atoms play the lead in the transitions, showing displacement in or transfer between the interstitial sites of a metal lattice. One example is the band gap closing observed for a long period lattice of yttrium tri-hydride, YH3, appearing at pressures above 12 GPa. Another example is photochromic event observed again for yttrium hydride, YHx. The former is likely accompanied by the in-site displacement of hydrogen atoms and the latter by the site-to-site transfer.

DOI： 10.4131/jshpreview.18.273

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Language：English   Publisher：AMER PHYSICAL SOC  

The pressure-induced structural transition of YH3 has been investigated by x-ray diffraction experiments under hydrostatic pressure at room temperature. The diffraction patterns of the intermediate state between the hexagonal and cubic phases are interpreted in terms of long-period polytypes with the periodic arrangements of hexagonal-type and fcc-type stacking layers of the Y metals. The hydrogen-hydrogen repulsive interactions and hydrogen-metal bonding likely play a dominant role in the gradual hexagonal-fcc lattice conversion via the long-period polytypic structures.

DOI： 10.1103/PhysRevB.76.052101

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Language：English   Publisher：AMERICAN PHYSICAL SOC  

Infrared vibrational absorption spectra are measured for yttrium trihydride at room temperature and pressures up to 30 GPa. The spectral change that begins near 12 GPa is interpreted in terms of a hcp-fcc structural transition, which agrees with previous x-ray diffraction measurements. For the hydrogen vibrations in the low-pressure hcp phase, the mode Gruneisen parameters are derived from the observed peak frequency shifts with pressure and the reported bulk modulus. The value of 1.91 for the octahedral-site vibration is three times larger than those for the tetrahedral-site vibrations, suggesting hybridization between the hydrogen 1s and yttrium 4d orbitals at the octahedral site. The infrared transmission spectra collapse when the high-pressure fcc phase is compressed beyond 23 GPa. The band gap abruptly closes without a structural change in the fcc metal lattice. The experimental results are in contrast to the previous theoretical calculations predicting the electronic transition either with hcp-fcc structural change or in the hcp low-pressure phase without structural change. The transition mechanism is still inconclusive.

DOI： 10.1103/PhysRevB.73.104105

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Event date： 2015

Language：Japanese  

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