Structural phase transition of ScSb and YSb with a NaCl-type structure at high pressures

By use of synchrotron radiation, powder X-ray diffraction of ScSb and YSb with a NaCl-type structure has been studied up to 45 GPa at room temperature. A first-order phase transition from the NaCl-type (B1) to a CsCl-type structure (B2) began to occur at around 28 GPa for ScSb and at around 26 GPa for YSb. Crystal data of the high-pressure phase of both antimonides are obtained. The high-pressure structural behavior of ScSb and YSb is similar to that of heavier LnSb (Ln=Dy-Lu). The B1-B2 transition for ScSb and YSb can be understood according to the rigid sphere model. The bulk moduli of ScSb and YSb are about 58 GPa at ambient pressure.     

Ca2CuO3的高压结构性质研究

 采用金刚石压砧高压装置（DAC）,对具有Cu—O链结构的Ca₂CuO₃的多晶粉末样品进行了高压同步辐射能散X射线衍射实验。实验结果表明,在0～34 GPa压力范围内,Ca₂CuO₃晶体没有发生结构相变,用Birch-Murnaghan状态方程拟合,得到在压力导数B′₀=4时,零压体弹模量B₀=165.4±1.8 GPa。     

Zn2SnO4纳米线高压下的相变研究

 利用金刚石对顶压砧（DAC）对具有反尖晶石结构的透明导体氧化物Zn₂SnO₄（ZTO）纳米线进行了原位高压同步辐射角散X射线衍射（ADXRD）研究。结果发现：在压力为12.9 GPa附近,晶体的对称性降低,并发生晶体结构相变,产生中间过渡相;当压力为32.7 GPa时,发生高压相变,形成高压相。在样品加压前后,纳米线的形貌发生了很大的变化。通过Birch-Murnaghan方程,拟合得到B′₀=4时的体弹模量B₀ =(168.6±9.7) GPa。     

Phase transition of ZnS at high pressures and temperatures

The high-pressure behaviour of zinc sulphide, ZnS, has been investigated, using an in situ X-ray powder diffraction technique in a diamond anvil cell, at pressures and temperatures up to 35 GPa and 1000 K, respectively. The pressure-induced phase transition from a zincblende (B3) to a rocksalt (B1) structure was observed. This transition occurred at 13.4 GPa and at room temperature, and a negative dependence on temperature for this transition was confirmed. The transition boundary was determined to be P (GPa) = 14.4 ? 0.0033 × T (K).     

六角相B-C-N化合物的高压相变研究

采用原位高压同步辐射能散X射线衍射和金刚石压砧技术,实验研究了新型超硬材料六角相B0.47C0.23N0.30的高压相变及物理特性,压力范围为1.4～30 GPa.实验结果表明,六角相B..47C0.23N0.30在14.9 GPa压力下发生了相变,形成的新相为六方纤锌矿结构.计算得到了具有六方纤锌矿结构的B0.47C...     

Evidence of polymorphic transformations of Sn under high pressure

The high-pressure polymorphs and structural transformation of Sn were experimentally investigated using angledispersive synchrotron x-ray diffraction up to 108.9 GPa. The results show that at least at 12.8 GPa β-Sn→bct structure transformation was completed and no two-phase coexistence was found. By using a long-wavelength x-ray, we resolved the diffraction peaks splitting and discovered the formation of a new distorted orthorhombic structure bco from the bct structure at 31.8 GPa. The variation of the lattice parameters and their ratios with pressure further validate the observation of the bco polymorph. The bcc structure appears at 40.9 GPa and coexists with the bco phase throughout a wide pressure range of40.9 GPa–73.1 GPa. Above 73.1 GPa, only the bcc polymorph is observed. The systematically experimental investigation confirms the phase transition sequence of Sn as β-Sn→bct→bco→ bco + bcc→bcc upon compression to 108.9 GPa at room temperature.     

Study of partial melting at high-pressure using in situ X-ray diffraction

The high-pressure melting behavior of different iron alloys was investigated using the classical synchrotron-based in situ X-ray diffraction techniques. As they offer specific advantages and disadvantages, both energy-dispersive (EDX) and angle-dispersive (ADX) X-ray diffraction methods were performed at the BL04B1 beamline of SPring8 (Japan) and at the ID27-30 beamline of the ESRF (France), respectively. High-pressure vessels and pressure ranges investigated include the Paris–Edinburgh press from 2 to 17 GPa, the SPEED-1500 multi-anvil press from 10 to 27 GPa, and the laser-heated diamond anvil cell from 15 to 60 GPa. The onset of melting (at the solidus or eutectic temperature) can be easily detected using EDX because the grains start to rotate relative to the X-ray beam, which provokes rapid and drastic changes with time of the peak growth rate. Then, the degree of melting can be determined, using both EDX and ADX, from the intensity of diffuse X-ray scattering characteristic of the liquid phase. This diffuse contribution can be easily differentiated from the Compton diffusion of the pressure medium because they have different shapes in the diffraction patterns. Information about the composition and/or about the structure of the liquid phase can then be extracted from the shape of the diffuse X-ray scattering.     

Pressure-induced phase transitions of lanthanide monoarsenides LaAs and LuAs with a NaCl-type structure

By use of synchrotron radiation the powder X-ray diffraction of lanthanide monoarsenides LaAs and LuAs with a NaCl-type structure has been studied up to 60 GPa at room temperature. First-order phase transitions with the crystallographic change were found at around 20 GPa for LaAs, and 57 GPa for LuAs. The high-pressure form of LaAs is a tetragonal structure and can be viewed as a distorted CsCl-type structure. The atoms in the tetragonal structure are located at La: 0, 0, 0; As: 1/2, 1/2, 1/2. The space group is P4/mmm. The structural change to the tetragonal structure occurs with the volume collapse of about 10%. The structure of these high-pressure phases of LuAs is unknown. The volume vs. pressure curves for LaAs and LuAs are fitted by a Birch equation of state. The bulk moduli of both arsenides are 92±6 GPa for LaAs and 85±3 GPa for LuAs. The high-pressure structural behavior of LaX (X=P, As and Sb) and LnAs (Ln=lanthanide) with the NaCl-type structure is discussed.     

Equation of state and thermal expansivity of LiF and NaF

The high-pressure and high-temperature behaviors of LiF and NaF have been studied up to 37 GPa and 1000 K. No phase transformations have been observed for LiF up to the maximum pressure reached. The B1 to B2 transition of NaF at room temperature was observed at ～28 GPa, this transition pressure decreases with temperature. Unit-cell volumes of LiF and NaF B1 phase measured at various pressures and temperatures were fitted using a P–V–T Birch–Murnaghan equation of state. For LiF, the determined parameters are: α₀ = 1.05 (3)×10^?4 K^?1, dK/dT = ?0.025 (2) GPa/K, V ₀ = 65.7 (1) Å³, K ₀ = 73 (2) GPa, and K′ = 3.9 (2). For NaF, α₀ = 1.34 (4)×10^?4 K^?1, dK/dT = ?0.020 (1) GPa/K, V ₀ = 100.2 (2) Å³, K ₀ = 46 (1) GPa, and K′ = 4.5 (1).     

Pressure-dependent phase transition in the ordered BaBi0.7Nb0.3O3 perovskite

BaBi_0.7Nb_0.3O₃, an ordered perovskite, crystallizes in a centrosymmetric rhombohedral structure with the space group R3¯. The refined cell parameters obtained from synchrotron powder X-ray diffraction data for the rhombohedral phase at ambient pressure are a=6.109 (2) Å and α=60.3 (1)°. The pressure-dependent synchrotron powder X-ray diffraction studies show a phase transition around 8.44±1 GPa, where it transforms from rhombohedral structure to a monoclinic structure. The lattice parameters obtained for the monoclinic phase at a pressure of 15±1 GPa are a=5.91 (2) Å, b=6.25 (3) Å and c=8.22 (1) Å with monoclinic angle, β=88 (1)°.     

Phase transitions of YbX (X = P,As and Sb) with a NaCl-type structure at high pressures

The powder X-ray diffraction of YbX (X?=?P, As and Sb) with a NaCl-type structure has been studied with synchrotron radiation up to 63?GPa at room temperature. YbSb undergoes the first-order structural phase transition from the NaCl-type (B1) to the CsCl-type (B2) structure at around 13?GPa. The structural change to the B2 structure occurs with the volume collapse of about 1% at 13?GPa. The transition pressure of YbSb is surprisingly lower than that of any other heavier LnSb (Ln?=?Dy, Ho, Er, Tm and Lu). The pressure-induced phase transitions in YbP and YbAs are observed at around 51?GPa and 52?GPa respectively. The transition pressure of both compounds is much higher than that of YbSb. The high-pressure structural behaviour of YbX (X?=?P, As and Sb) is discussed. The volume versus pressure curve for YbX with the NaCl-type structure is fitted by a Birch equation of state. The bulk moduli of these compounds with the NaCl-type structure are 104?GPa for YbP, 85?GPa for YbAs and 52?GPa for YbSb.     

Phase transitions in KIO(3)

The high-pressure behavior of KIO(3) was studied up to 30?GPa using single crystal and powder x-ray diffraction, Raman spectroscopy, second harmonic generation (SHG) experiments and density functional theory (DFT)-based calculations. Triclinic KIO(3) shows two pressure-induced structural phase transitions at 7?GPa and at 14?GPa. Single crystal x-ray diffraction at 8.7(1)?GPa was employed to solve the structure of the first high-pressure phase (space group R3, a?=?5.89(1) ?, α?=?62.4(1)°). The bulk modulus, B, of this phase was obtained by fitting a second order Birch-Murnaghan equation of state (eos) to synchrotron x-ray powder diffraction data resulting in B(exp,second)?=?67(3)?GPa. The DFT model gave B(DFT,second)?=?70.9?GPa, and, for a third order Birch-Murnaghan eos, B(DFT,third)?=?67.9?GPa with a pressure derivative of [Formula: see text]. Both high-pressure transformations were detectable by Raman spectroscopy and the observation of second harmonic signals. The presence of strong SHG signals shows that all high-pressure phases are acentric. By using different pressure media, we showed that the transition pressures are very strongly influenced by shear stresses. Earlier work on low- and high-temperature transitions was complemented by low-temperature heat capacity measurements. We found no evidence for the presence of an orientational glass, in contrast to earlier dielectric studies, but consistent with earlier low-temperature diffraction studies.     

A new high-pressure phase of ZnSe with B9-type structure

High-pressure and high-temperature behavior of ZnSe was investigated by energy dispersive X-ray diffraction method up to 14 GPa and 800°C. A new high-pressure phase with B9 (HgS)-type structure is found near the B3-B1 phase boundary at room temperature, as predicted by an ab-initio calculation. The property and observed pressure region of the B9-type phase are in good agreement with the ab-initio calculation. At high-temperature condition above 300°C, only the direct transitions are observed between the B3 and B1 phases. The B3-B1 phase boundary is also determined to be P (GPa)=12.21−0.0039T (°C) for the temperature range between 300 and 800°C.     

Equation of state and electrical resistivity of the heavy fermion superconductor CeCoIn<Subscript>5</Subscript> to 51 GPa

We have used X-ray diffraction to study the structural phase of CeCoIn₅ in external pressure. Using high-pressure X-ray diffraction, we find that the crystalline phase is stable in the P4/mmm phase for pressures ≤51.2 GPa. From our measured equation of state, we find a bulk modulus given by B ₀ = 72.8 ± 2.9 GPa and a first pressure derivative of B ^′ = 5.1 ± 0.3. Measurement of the electrical resistivity of CeCoIn₅ to pressures as high as 34.4 GPa shows the existence of a peak in resistivity at p ^? = 8.2 ± 0.2 GPa.     

Effects of pressure on the two polymorphs of [Co(NH3)5NO2]I2: The anisotropy of lattice distortion and a phase transition

Abstract

The effect of pressure on the two polymorphs of [CO(NH₃)₅NO₂]I₂ (phase I-orthorhombic, S.G. Pnma; phase II-monoclinic, S.G. C2/m) was studied by X-ray powder diffraction in a diamond anvil cell (DAC). In the presence of the ethanol-methanol-water mixture used as a pressure-transmitting liquid polymorph I was shown to undergo a phase transition at pressures between 0.45 GPa and 0.65 GPa. The diffraction pattern of the high-pressure phase (phase III) could be indexed as tetragonal with lattice parameters similar to those, which were previously reported for polymorph II in a 'pseudotetragonal setting'. The lattice distortions of phases II and III were studied at pressures up to 3.2 GPa and 3.7 GPa, correspondingly, and were shown to be very similar. Phases II and III were supposed to be very closely related. If poly(chlortrifluorethylen)-oil was used as a pressure-transmitting medium, no phase transitions were observed in phase I of [CO(NH₃)₅NO₂I₂ at least up to 1.8 GPa (the point when poly(chlortrifluorethylen)-oil becomes solid), and the anisotropy of lattice distortion could be measured.     

Phase Relations and EOS of ZrO 2 and HfO 2 Under High-temperature and High-pressure

The phase relations and equations of state of ZrO 2 and HfO 2 high-pressure polymorphs have been investigated by means of in situ observation using multi-anvil type high-pressure devices and synchrotron radiation. Baddeleyite (monoclinic ZrO 2 ) transforms to two distorted fluorite (CaF 2 )-type phases at 3-4 GPa depending on temperature: an orthorhombic phase, orthoI, below 600 °C and a tetragonal phase, which is one of the high-temperature forms of ZrO 2 , above 600 °C. Both orthoI and tetragonal phases then transform into another orthorhombic phase, orthoII, with a cotunnite (PbCl 2 )-type structure above 12.5 GPa and the phase boundary is almost independent of temperature. OrthoII is stable up to 1800 °C and 24 GPa. In case of HfO 2 , orthoI is stable from 4 to 14.5 GPa below 1250-1400 °C and transforms to the tetragonal phase above these temperatures. OrthoII of HfO 2 appears above 14.5 GPa and is stable up to 1800 °C at 21 GPa. The unit cell parameters and the volumes of these high-pressure phases have been determined as functions of pressure and temperature. The orthoI/tetragonal-to-orthoII transition of both ZrO 2 and HfO 2 is accompanied by about 9% volume decrease. The bulk moduli of orthoII calculated using Birch-Murnaghan's equations of state are 296 GPa and 312 GPa for ZrO 2 and HfO 2 , respectively. Since orthoII of both ZrO 2 and HfO 2 are quenchable to ambient conditions, these are candidates for super-hard materials.     

Pressure induced phase transition in MnTe2

Energy dispersive high-pressure powder X-ray experiments have been performed for MnTe₂ up to a pressure of 20 GPa. MnTe₂ undergoes a discontinuous transformation from the cubic pyrite type structure to the orthorhombic marcasite type structure at 7.0±0.5 GPa upon increasing pressure. The transformation is accompanied by a large reduction in the specific volume (ΔV/V=0.18) which probably reflects different magnetic properties of the two modifications of MnTe₂.     

Crystallographic and magnetic structure of HAVAR under high-pressure using diamond anvil cell (DAC)

Annealed (H1) and cold-rolled (H2) HAVAR has been studied using high-pressure synchrotron X-ray diffraction. A structural phase transformation was discovered at ～13 GPa at ambient temperature, transforming from m ??3 m (S.G. 225) to P 63/m m c (S.G. 194) symmetry. The transition was not reversible on pressure release. The low-pressure cubic phase was found to be more compressible than the high-pressure hexagonal phase. Conventional Mössbauer and NFS shows that the HAVAR is not magnetic at room temperature and no splitting is observed. The SQUID indicates a huge difference in the temperature dependence of the magnetic susceptibility between the cold Rolled HAVAR compared to the annealed HAVAR.     

Study of phase transition on nanocrystalline (La, Sr)(Mn, Fe)O system using high-pressure Mössbauer spectroscopy and high-pressure X-ray diffraction

Pressure-induced structural changes on nano-crystalline La_0.8Sr_0.2Mn_0.8Fe_0.2O₃ were studied using high-pressure Mössbauer spectroscopy and high-pressure X-ray diffraction. Mössbauer measurements up to 10 GPa showed first order transition at 0.52 GPa indicating transformation of Fe^4?+? to high spin Fe^3?+?, followed by another subtle transition at 3.7 GPa due to the convergence of two different configurations of Fe into one. High-pressure X-ray diffraction measurements carried up to 4.3 GPa showed similar results at 0.6 GPa as well as 3.6 GPa. Attempts were made to explain the changes at 0.6 GPa by reorientation of grain/grain boundaries due to uniaxial stress generated on the application of pressure. Similarly variation at 3.6 GPa can be explained by orthorhombic to monoclinic transition.     

Synchrotron X-ray diffraction of SiO2 to multimegabar pressures

Abstract

α-Quartz was compressed at room temperature in a diamond-anvil cell without a medium to maximum pressures of 31 to 213 GPa and was studied by energy-dispersive synchrotron X-ray diffraction. Broad peaks observed in a previous high-pressure diffraction study of silica glass are evident in the present study of quartz compression, providing in situ confirmation of pressure-induced amorphization above 21 GPa. The 21-GPa crystalline-crystalline (quartz 1–11) transformation previously observed on quasihydrostatic compression of quartz is found to also occur under the current nonhydrostatic conditions, at the identical pressure. With nonhydrostatic compression, however, new sharp diffraction lines are observed at this pressure. The measurements show the coexistence of at least one amorphous and two crystalline phases above 21 GPa and below 43 GPa. The two crystalline phases are identified as quartz II and a new, high-pressure silica phase. The high-pressure phases, both crystalline and amorphous, can be quenched to ambient conditions from a maximum pressure of 43 GPa. With compression above 43 GPa, the diffraction pattern from quartz II is lost and the second crystalline phase persists to above 200 GPa.