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Layered transition-metal trichalcogenides have become one of the research frontiers as two-dimensional magnets and candidate materials used for phase-change memory devices. Herein we report the high-pressure synchrotron X-ray diffraction and resistivity measurements on Cr2Ge2Te6 (CGT) single crystal by using diamond anvil cell techniques, which reveal a mixture of crystalline-to-crystalline and crystalline-to-amorphous transitions taking place concurrently at 18.3-29.2 GPa. The polymorphic transition could be interpreted by atomic layer reconstruction and the amorphization could be understood in connection with randomly flipping atoms into van der Waals gaps. The amorphous (AM) phase is quenchable to ambient conditions. The electrical resistance of CGT shows a bouncing point at ~ 18 GPa, consistent with the polymorphism phase transition. Interestingly, the high-pressure AM phase exhibits metallic resistance with the magnitude comparable to that of high-pressure crystalline phases, whereas the resistance of the AM phase at ambient pressure fails to exceed that of the crystalline phase, indicating that the AM phase of CGT appeared under high pressure is quite unique and similar behavior has never been observed in other phase-change materials. The results definitely would have significant implications for the design of new functional materials., 14 pages,7 figures, 2 tables, 1 supporting information. JPCC in press

Orthorhombic (space group: Pnma) Nb2P5 is a high-pressure phase that is quenchable to ambient pressure, which could viewed as the zigzag infinite P chain-inserted NbP2. We report herein the high-pressure crystal growth of Nb2P5 and the discovery of its superconducting transition at Tc ~ 2.6 K. The electrical resistivity, magnetization, and specific heat capacity measurements on the high-quality crystal unveiled a conventional type-II weakly coupled s-wave nature of the superconductivity, with the upper critical field Hc2(0) ~ 0.5 T, the electron-phonon coupling strength {\lambda}ep ~ 0.5 - 0.8, and the Ginzburg-Landau parameter \k{appa} ~ 100. The ab initio calculations on the electronic band structure unveiled nodal-line structures protected by different symmetries. The one caused by band inversion, for example, on the {\Gamma}-X and U-R paths of the Brillouin zone, likely could bring nontrivial topology and hence possible nontrivial surface state on the surface. The surface states on the (100), (010) and (110) surfaces were also calculated and discussed. The discovery of the phosphorus-rich Nb2P5 superconductor would be instructive for the design of more metal phosphides superconductors which might host unconventional superconductivity or potential technical applications., Comment: 8 pages,8 figures in the main text + 4 pages, 3 figures, 1 table in the supplementary information

Morphotropic phase boundaries (MPB) consisting of rhombohedral and orthorhombic phases formed within the range of 0.1 ≤ x ≤ 0.15 in Bi1-xErxFe0.97Ti0.03O3 ceramics. Orthorhombic phase transition was verified by the appearance of a new mode at 310 cm−1 in Raman spectra. Bridging phases as intermedia phases of MPB were rare in Bi1-xErxFe0.97Ti0.03O3. Polarization and permittivity improved at MPB. Moreover, impedance spectroscopy revealed additional arcs with a distinct small polaron conduction mechanism. Er3+ ions enhanced magnetic properties and induced a permittivity change at Neel temperature. The magnetodielectric effect resulted in a permittivity change rate of ~1% at 10000 Oe.

Topological semimetal, a novel state of quantum matter hosting exotic emergent quantum phenomena dictated by the nontrivial band topology, has emerged as a new frontier in condensed-matter physics. Very recently, the coexistence of triply degenerate points of band crossing and Weyl points near the Fermi level was theoretically predicted and experimentally identified in MoP. Via high-pressure electrical transport measurements, we report here the emergence of pressure-induced superconductivity in MoP with a critical transition temperature Tc of ca. 2.5 K at ca. 30 GPa. No structural phase transition is observed up to ca. 60 GPa via synchrotron X-ray diffraction study. Accordingly, the topologically nontrivial band protected by the crystal structure symmetries and superconductivity are expected to coexist at pressures above 30 GPa, consistent with density functional theory calculations. Thus, the pressurized MoP represents a promising candidate of topological superconductor. Our finding is expected to stimulate further exploitation of exotic emergent quantum phenomena in novel unconventional fermion system. Molybdenum phosphide becomes superconducting above 30 GPa, with a critical transition temperature of 2.5 K. A team led by Youguo Shi, Xiaoping Yang and Zhaorong Yang from the Chinese Academy of Sciences perform high-pressure electrical transport measurements in molybdenum phosphide, which is a recently proved topological material hosting exotic fermions. They apply pressure over 90 GPa and observe a superconducting transition above 30 GPa with a critical transition temperature of 2.5 K, which increases to 4 K at 95 GPa. Meanwhile, the compound crystalizes into a (tungsten carbide) WC-type structure where the topological properties are predicted from ambient pressure up to 60 GPa. They expect that topological fermions and superconductivity could coexist under a pressure between 30 GPa and 60 GPa, suggesting a possible candidate for topological superconductivity.

Manganese (Mn)-based antiperovskite structures (Mn3AX, where A and X represent the 3d transition-metal elements and N or C atoms, respectively) have attracted growing attention because of their novel electronic and magnetic properties. However, the lack of an effective approach to regulate the magnetic coupling in Mn3AX crystal structure, particularly in antiferromagnetic ground states, hinders their further design and applications. Herein, robust high-temperature ferrimagnetic order with a Curie temperature (TC) in the range of ∼390–420 K was successfully achieved in Mn3GaxNx (x = 0.5, 0.6, and 0.7) via composition-deficient engineering. A systematic investigation, including synchrotron X-ray diffraction, neutron powder diffraction, pair distribution function, X-ray absorption near-edge structure, magnetic characterization, and first-principles calculations, convincingly indicated that the redistribution of partial atoms in the antiferromagnetic ground state was responsible for the observed long-range magnetic order. These results not only provide a new perspective into the design and construction of high-temperature ferrimagnets based on the Mn3AX structure, but also open up a promising avenue for the further design of Mn3AX-based spintronic or other multifunctional devices.

In this study, a series of Bi2Te2-xS1+x compounds were prepared by traditional melting-quenching-annealing process. In the range of 0.03 ≤ x ≤ 0.25, Bi2Te2-xS1+x compounds possess the Bi2Te3 structure. S atoms preferentially fully occupy the Te(2) sites, while any extra S atoms randomly occupy the Te(1) sites. Experimental results and phonon dispersion calculations demonstrate that the strong coupling of the phonon density of state contributed by Bi and Te(1) atoms results in the low avoided-crossing frequencies, sound velocities, Debye temperature and therefore the low lattice thermal conductivities. Moreover, substitutions of extra S atoms on the Te(1) site intensifies alloy phonon scattering that further suppresses the lattice thermal conductivity. An ultra-low lattice thermal conductivity of 0.49 W m−1 K−1 is achieved at 523 K. Doping with Cl increases the room temperature carrier concentration, resulting in a significantly enhanced power factor from 1.5 mW m−1 K−2 for the Bi2Te1.93S1.07 sample to 1.7 mW m−1 K−2 for the Cl-doped sample at 323 K. Furthermore, doping with Cl enhances phonon point defect scattering that leads to a suppression of the thermal conductivity to 0.41 W m−1 K−1 at 573 K. As a result of the optimization of the electronic transport properties and the reduction in the lattice thermal conductivity, Bi2Te1.93S1.065Cl0.005 sample achieved the highest ZT of 0.67 at 623 K which is superior to intrinsic Bi2Te3 in the whole temperature range.

In this paper, a novel composite La0.9Ca0.1Fe0.9Nb0.1O3-δ/Sc0.2Zr0.8O2−δ (LCFNb/ScSZ) is developed and investigated as a fuel electrode candidate for direct electrolyzing carbon dioxide (CO2) in solid oxide electrolysis cells (SOECs). XRD patterns of LCFNb powder sintered in CO2 at 850 °C for 10 h indicate that no secondary phases are found during the heat treatment and linear thermal expansion results prove that the LCFNb is compatible with ScSZ electrolyte used in this work. The electrolyser with porous LCFNb membrane cathode fabricated by infiltration method shows impressive electrochemical performance. The current density of 1.97 A/cm2 at 2.0 V at 800 °C is obtained. The polarization resistance Rp of the SOEC decreases with the increase of the applied voltage between the electrodes. The obtained lowest Rp is as low as 0.113 Ω cm2 at 2.0 V and this value is much lower than its many other perovskite and nickle-based counterparts. Besides, the LCFNb/ScSZ cathode shows excellent stability in pure CO2 at different applied voltage, especially at 2.0 V. Furthermore, the LCFNb/ScSZ electrode exhibits the current efficiencies close to theoretical ones for CO2 electrolysis, indicating that the LCFNb/ScSZ composite ceramic is an excellent cathode for zirconia-based high temperature electrolyser.

(Gadolinium) Gd-doped antiperovskite compounds Mn 3 Cu 1−x Gd x N were synthesized by the conventional solid-state reaction. With increasing Gd concentration, two magnetic transitions appeared at a high Curie temperature (T C1 ) corresponding to paramagnetic (PM)-ferromagnetic (FM) transition and a low temperature (T C2 ) ascribed to the FM-antiferromagnetic (AFM) transition. The magnetic relaxation results show the formation of a magnetic metastable state after the FM-AFM transition at low temperature (lower than T C2 ), forming a novel magnetic-step feature in the process from AFM to FM under a certain magnetic field.

We report the discovery of superconductivity in high-quality single crystals of transition-metal pnictides WP grown by chemical vapor transport method. Bulk superconductivity is observed at ${T}_{\text{c}}\ensuremath{\sim}0.8\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ at ambient pressure by electrical resistivity, ac magnetic susceptibility, and specific-heat measurements. The effects of magnetic field on the superconducting transitions are studied, leading to a large anisotropy parameter around 2 with the in-plane and out-of-plane upper critical fields of ${\ensuremath{\mu}}_{0}{H}_{\text{c}2,\ensuremath{\parallel}}=17.2\phantom{\rule{0.28em}{0ex}}\mathrm{mT}$ and ${\ensuremath{\mu}}_{0}{H}_{\text{c}2,\ensuremath{\perp}}=8.5\phantom{\rule{0.28em}{0ex}}\mathrm{mT}$, respectively. The low value of electron-phonon coupling estimated from the normal-state resistivity and specific-heat measurements suggest that WP is a weak-coupling BCS superconductor. Our finding demonstrates that WP is the first superconductor among $5d$--transition metal pnictides with MnP-type structure at ambient pressure, which will help in the search for new superconductors in transition-metal pnictides.

We systematically investigate the influence of high pressure on the electronic transport properties of layered ferromagnetic materials; in particular, those of ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$. Its crystal sustains a hexagonal phase under high pressures up to 25.9 GPa, while the Curie temperature decreases monotonously with the increasing pressure. By applying appropriate pressures, the experimentally measured anomalous Hall conductivity, ${\ensuremath{\sigma}}_{xy}^{A}$, can be efficiently controlled. Our theoretical study reveals that this finding can be attributed to the shift of the spin--orbit-coupling-induced splitting bands of Fe atoms. With loading compression, ${\ensuremath{\sigma}}_{xy}^{A}$ reaches its maximal value when the Fermi level lies inside the splitting bands and then attenuates when the splitting bands float above the Fermi level. Further compression leads to a prominent suppression of the magnetic moment, which is another physical cause of the decrease in ${\ensuremath{\sigma}}_{xy}^{A}$ at high pressure. These results indicate that the application of pressure is an effective approach in controlling the anomalous Hall conductivity of layered magnetic materials, which elucidates the physical mechanism of the large intrinsic anomalous Hall effect.

The high-pressure effect on valence fluctuation of the ThCr2Si2-type intermetallic compound EuNi2P2 has been investigated using in situ synchrotron Mossbauer spectroscopy (SMS). The isomer shift of 151Eu in EuNi2P2 increases monotonically with increasing pressure up to 50 GPa, suggesting a valence transition of the Eu from mixed toward trivalent. The synchrotron angle-dispersive X-ray diffraction (AD-XRD) experiment shows that EuNi2P2 remains in the tetragonal structure up to 32.5 GPa at room temperature. We propose that the evolutions of bonding distance with pressure have an obvious effect on the valence fluctuation.

The extremely large magnetoresistance (XMR) in nonmagnetic semimetals has inspired growing interest owing to both intriguing physics and potential applications. We report results of synchrotron X-ray diffraction (SXRD) and electrical transport measurements on TaAs2 under pressure up to ~ 37 GPa, which revealed an anisotropic compression of the unit cell, formation of unusual As-As bonds above 9.5 GPa, and enhancement of metallicity. Interestingly, the MR of TaAs2 under pressure changed gently, which at 1.7 GPa is 96.6% and at 36.6 GPa is still 36.7%. The almost robust MR under pressure could be related to the nearly stable electronic structure unveiled by the ab initio calculations. The discovery would expand the potential use of XMR even under high pressure., Comment: 15 pages, 7 figures including those in supporting information

The layered Cr2Ge2Te6 (CrGT) has captured vast attentions because it is capable of retaining the long-range ferromagnetic order even in its monolayer form, thus offering potential applications in spintronic devices. We report herein the Raman spectra of CrGT under pressure up to 35.1 GPa at room temperature. We observed a structural phase transition at ∼14 GPa as was revealed by a change in pressure derivate frequencies of the E g 3 and A g 1 modes. Both of the two peaks became broad and the A g 1 mode eventually disappeared with further increasing the pressure. Raman modes above 26.4 GPa could not be experimentally observed, suggesting that the CrGT was pressed into the amorphous phase. Interestingly, a pressure-induced soft phonon mode is identified in CrGT at ∼23 GPa by dynamical property calculation. The phonon instability at the Brillouin zone boundary T point is suggested as the driving force for the experimentally observed crystalline-to-crystalline phase transition at ∼ 18 GPa. The appearance of soft phonon might indicate the possibility of superconductivity induced by much higher pressure.

CrAs was observed to possess the bulk superconductivity under high-pressure conditions. To understand the superconducting mechanism and explore the correlation between the structure and superconductivity, the high-pressure structural evolution of CrAs was investigated using the angle-dispersive X-ray diffraction (XRD) method. The structure of CrAs remains stable up to 1.8 GPa, whereas the lattice parameters exhibit anomalous compression behaviors. With increasing pressure, the lattice parameters a and c both demonstrate a nonmonotonic change, and the lattice parameter b undergoes a rapid contraction at similar to 0.18-0.35 GPa, which suggests that a pressure-induced isostructural phase transition occurs in CrAs. Above the phase transition pressure, the axial compressibilities of CrAs present remarkable anisotropy. A schematic band model was used to address the anomalous compression behavior of CrAs. The present results shed light on the structural and related electronic responses to high pressure, which play a key role toward understanding the superconductivity of CrAs.

As a follow-up of our previous work on pressure-induced metallization of the 2H_{c}-MoS_{2} [Chi et al., Phys. Rev. Lett. 113, 036802 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.036802], here we extend pressure beyond the megabar range to seek after superconductivity via electrical transport measurements. We found that superconductivity emerges in the 2H_{a}-MoS_{2} with an onset critical temperature T_{c} of ca. 3 K at ca. 90 GPa. Upon further increasing the pressure, T_{c} is rapidly enhanced beyond 10 K and stabilized at ca. 12 K over a wide pressure range up to 220 GPa. Synchrotron x-ray diffraction measurements evidenced no further structural phase transition, decomposition, and amorphization up to 155 GPa, implying an intrinsic superconductivity in the 2H_{a}-MoS_{2}. DFT calculations suggest that the emergence of pressure-induced superconductivity is intimately linked to the emergence of a new flat Fermi pocket in the electronic structure. Our finding represents an alternative strategy for achieving superconductivity in 2H-MoS_{2} in addition to chemical intercalation and electrostatic gating.

The influence of external pressure on the structural properties of manganese monophosphides (MnP) at room temperature has been studied using in situ angle dispersive synchrotron x-ray powder diffraction (AD-XRD) with a diamond anvil cell. The crystal structure of MnP is stable between 0 to 15 GPa. However, the compressibility of b-axis is much larger than those of a- and c-axes. From this result we suggested that the occurrence of superconductivity in MnP was induced by suppression of the long-range antiferromagnetically ordered state rather than a structural phase transition. Furthermore, the present experimental results show that the Pnma phase of MnP undergoes a pressure-induced structural phase transition at ~15.0 GPa. This finding lighted up-to-date understanding of the common prototype B31 structure (Strukturbericht Designation: B31) in transition metal monophosphides. No additional structural phase transition was observed up to 35.1 GPa (Run 1) and 40.2 GPa (Run 2) from the present AD-XRD results. With an extensive crystal structure searching and ab initio calculations, we predict that MnP underwent two pressure-induced structural phase transitions of Pnma → P213 and P213 → Pm-3m (CsCl-type) at 55.0 and 92.0 GPa, respectively. The structural stability and the electronic structures of manganese monophosphides under high pressure are also briefly discussed.

Indium selenide (In2Se3) could be used as the phase-change random access memory device and thermoelectric material. The high-pressure investigations are important to the applications on In2Se3 and other A2B3-type materials. In this study, we performed the in situ angle-dispersive X-ray diffraction and Raman spectra experiments and the first-principle calculations on In2Se3 under high pressure, and observed a series of structure phase transitions from experiments and metallized phenomena from calculations. In2Se3 transforms from the original rhombohedral structure (phase I) to a distorted monoclinic structure (phase II) and further to a Bi2Te3-type structure (phase III) at about 0.81 and 5.02 GPa, respectively. And then, phase III′ of In2Se3 adopts a similar structure with phase III from about 20.6 GPa. At pressures above about 32.1 GPa, In2Se3 starts to crystallize into a defective Th3P4-type structure (phase IV). According to the first-principle calculations, the structural transitions in the compression...

High-pressure angle-dispersive X-ray diffraction experiments on iron-based superconductor Ce(O(0.84)F(0.16))FeAs were performed up to 54.9 GPa at room temperature. A tetragonal to tetragonal isostructural phase transition starts at about 13.9 GPa, and a new high-pressure phase has been found above 33.8 GPa. At pressures above 19.9 GPa, Ce(O(0.84)F(0.16))FeAs completely transforms to a high-pressure tetragonal phase, which remains in the same tetragonal structure with a larger a-axis and smaller c-axis than those of the low-pressure tetragonal phase. The structure analysis shows a discontinuity in the pressure dependences of the Fe-As and Ce-(O, F) bond distances, as well as the As-Fe-As and Ce-(O, F)-Ce bond angles in the transition region, which correlates with the change in T(c) of this compound upon compression. The isostructural phase transition in Ce(O(0.84)F(0.16))FeAs leads to a drastic drop in the superconducting transition temperature T(c) and restricts the superconductivity at low temperature. For the 1111-type iron-based superconductors, the structure evolution and following superconductivity changes under compression are related to the radius of lanthanide cations in the charge reservoir layer.

The 6H and 6M Ba 1− x Sr x RuO 3 at x ⩽0.6 with the normal and distorted hexagonal BaTiO 3 structures were synthesized by using high-pressure and high-temperature method. It is found that the unit cell volume deviates from Vegard's law between 0.3 and 0.4 for the solid solutions due to the increasing distortion degree of crystal structure. With the increasing x , the electrical resistivity at the same temperature is increasing. With the substitution of Sr for Ba ion, the 6H BaRuO 3 transforms to a Fermi-liquid metal at x =0.25 from the primal non-Fermi-liquid metal, and then becomes a semiconductor at low temperature when x is larger than 0.4.

The high-pressure phase of iridium-based compound Ba3CaIr2O9 was synthesized using high-pressure sintering. Being different from the distorted hexagonal BaTiO3 structure of the ambient Ba3CaIr2O9, the high-pressure phase crystals into the 1:2 B-site-ordered perovskite structure with the space group P-3m1 (Z=1). Through fitting the X-ray powder diffraction (XRD) data with Rietveld analysis, in which the obtained Rp, Rwp, and Rexp factors are 7.49%, 11.4%, and 4.82%, respectively, the lattice parameters are a=5.8296(1) A and c=7.1659(2) A. The atomic coordinates and the main interatomic distances and bond angles were also obtained. The relationship of electrical resistivity versus temperature shows that the high-pressure phase of Ba3CaIr2O9 is a semiconductor in the temperature range of 5–300 K. The measurement of temperature dependence of magnetic susceptibility indicates that it is paramagnetic.

The 6H BaRu{sub 1-x}Mn{sub x}O{sub 3} with the hexagonal BaTiO{sub 3} structure was synthesized using high-pressure sintering method. It is found that the lattice parameter deviates from Vegard's law at x=0.3 for the solid solutions due to the charge transfer effects at B-site. The substitution of Mn for Ru cations gives rise to the short-range magnetic ordering, due to the disordered arrangement of Ru and Mn cations. The compounds are weak ferromagnetic in the x range 0.05-0.40, with the maximal Curie temperature T{sub c} 175.2 K at x=0.10. They are of spin-glass-like magnetism at lower temperature at x{>=}0.1. With Mn doping, the 6H BaRuO{sub 3} transforms to a semiconductor from the primal metal at x=0.30. The resistance as a function of temperature below about 70 K follows the two-dimensional variable-range hopping conduction mechanism in BaRu{sub 0.50}Mn{sub 0.50}O{sub 3}. - Graphical abstract: The 6H BaRu{sub 1-x}Mn{sub x}O{sub 3} was synthesized using high-pressure sintering. The substitution of Mn for Ru cations gives rise to the short-range magnetic ordering, with the maximal Curie temperature T{sub c} 175.2 K at x=0.10. The compounds are of spin-class magnetism at lower temperature at x{>=}0.05. Mn doping results in the transition from the primal metal to semiconductormore » at x=0.30.« less

The single-phase 6H BaRuO{sub 3} with the hexagonal BaTiO{sub 3} structure was synthesized at 5 GPa and 1000 deg. C. Rietveld refinement of the powder X-ray data for the 6H phase resulted in the lattice parameters to be a=5.7127(1) A and c=14.0499(2) A; the average Ru-O distance and direct Ru-Ru distance in the Ru{sub 2}O{sub 9} dioctahedron being 1.992(6) and 2.5658(14) A, respectively. The electrical resistivity of the 6H BaRuO{sub 3} follows a relationship of {rho} versus T{sup 3/2} below 60.0 K, a signature deviation from the Fermi-liquid behavior. Both magnetic susceptibility and specific heat data indicate that the 6H BaRuO{sub 3} is an exchange-enhanced Pauli paramagnet due to the electron correlation effect with large Wilson ratio R{sub W} and Stoner enhancement factor. The comprehensive evolution of transport and magnetic properties from 9R across 4H to 6H BaRuO{sub 3} was discussed. - Graphical abstract: The single-phase 6H BaRuO{sub 3} was synthesized under high pressure high temperature. The electrical resistivity of 6H BaRuO{sub 3} follows a T{sup 3/2} relation below 60.0 K. Both magnetic susceptibility and specific heat data indicate that 6H BaRuO{sub 3} is an exchange-enhanced Pauli paramagnet with the large Wilson ratio and Stoner enhancement factor.

Silver nanocluster doped ZnO thin films were fabricated on fused quartz substrates at different temperatures by pulsed laser deposition (PLD) using a silver-ZnO mosaic target. X-ray diffraction (XRD) measurements showed that ZnO and doped silver nanoclusters crystallized with preferred c-axis orientation. Scanning electron microscopic (SEM) images of the sample fabricated at 450 degrees C and the X-ray photoelectron spectroscopy (XPS) showed the radius of the silver clusters to be about 3-16 nm. Under 266 nm laser excitation, the photoluminescence (PL) spectra exhibited a peak at 414-420 nm for silver nanocluster doped ZnO thin films deposited at different temperatures. Through the investigation of the energy level of the defects in ZnO thin films, the energy levels of the zinc vacancy (VznEVzn = 3.031eV) and the interstitial zinc atom (Zn-i, E-Zn, = 2.95 eV) were found to be consistent with the peak wavelengths of 414 and 420 run. We suggest that this violet emission originates from an electronic transition between the interstitial-zinc level and the valence band, or between the bottom of the conduction band and the V(Zn)level. (c) 2005 Elsevier B.V. All rights reserved.

Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr2S3) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr2S3 near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7–15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr2S3 based applications under extreme conditions.

The 6M BaIrO(3) with the distorted hexagonal BaTiO(3) structure was synthesized by high-pressure sintering. Through Rietveld refinement of the powder X-ray diffraction data, the lattice parameters of a = 5.7459(1) A, b = 9.9289(2) A, c = 14.3433(2) A, and beta = 91.340(1) degrees were obtained. In the Ir(2)O(9) dioctahedron, the average Ir-O distance and direct Ir-Ir distance were equal to 2.067(19) and 2.719(1) A, respectively. The temperature dependence of electrical resistivity shows that the 6M BaIrO(3) is a new metallic iridate. It is an abnormal metal, being deviated from the Fermi liquid behavior, following a linear relationship of rho versus T below 20 K. Both magnetic susceptibility and specific heat data indicate that it is an exchange-enhanced Pauli paramagnet, because of the electron-electron correlation effect.

The high-pressure angle-dispersive X-ray diffraction experiments on the iron-based superconductor Nd(O0.88F0.12)FeAs were performed up to 32.7 GPa at room temperature. An isostructural phase transition starts at approximately 10 GPa. When pressure is higher than 13.5 GPa, Nd(O0.88F0.12)FeAs completely transforms to a high-pressure phase, which remains the same tetragonal structure with a larger a-axis and smaller c-axis than those of the low-pressure phase. The ambient conditions isothermal bulk moduli B0 are derived as 102(2) and 245(9) GPa for the low-pressure phase and high-pressure phase, respectively. The structure analysis based on the Rietveld refinement methods shows the difference of pressure dependence of the Fe-As and Nd-(O, F) bonding distances, as well as As-Fe-As and Nd-(O, F)-Nd angles between the low-pressure phase and high-pressure phase.

Cu{sub 3}N band structures and phonon dispersion curves under pressure are calculated using first-principles density functional theory and density functional perturbation theory with the local density approximation by the plane-wave pseudopotential method. The band structures are similar to other full-potential calculations. The indirect band gap is about 0.13 eV and decreases with increasing pressure. Simultaneous softening of the M{sub 3} and R{sub 25} zone boundary phonon modes was found and the possible associated successive structural phase transitions were discussed. The mode Grueneisen parameters for optic modes were obtained and the frequency versus pressure relationship was well fitted to second-order polynomials. The quadric relationship between the soft-mode frequency and pressure was also well reproduced for the M{sub 3} and R{sub 25} soft modes. The large difference of the soft-mode-driven transition pressures for the first high-pressure phases of ReO{sub 3} and Cu{sub 3}N were also discussed.

The phase transition, amorphization, and crystallization behaviors of the topological insulator bismuth selenide (Bi2Se3) were discovered by performing in situ high-pressure angle-dispersive x-ray diffraction experiments during an increasing, decreasing, and recycling pressure process. In the compression process, Bi2Se3 transforms from the original rhombohedral structure (phase I(A)) to a monoclinic structure (phase II) at about 10.4 GPa, and further to a body-centered tetragonal structure (phase III) at about 24.5 GPa. When releasing pressure to ambient conditions after the complete transformation from phase II to III, Bi2Se3 becomes an amorphous solid (AM). In the relaxation process from this amorphous state, Bi2Se3 starts crystallizing into an orthorhombic structure (phase I(B)) about five hours after releasing the pressure to ambient. A review of the pressure-induced phase transition behaviors of A2B3-type materials composed from the V and VI group elements is presented.