High-pressure Angle-dispersive X-ray Research Articles

High-pressure phase transitions, amorphization, and crystallization behaviors in Bi2Se3

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.

Structural stability of URh3 at high pressure

URh3 stabilizes in the cubic AuCu3 type structure at normal temperature and pressure. High-pressure angle-dispersive X-ray diffraction experiments were performed on URh3 up to 25GPa using a diamond-anvil cell. URh3 remains in its cubic AuCu3 type structure up to the maximum pressure studied. The Birch–Murnaghan equation of state fit to the P–V data yields the bulk modulus to be 133GPa. The Villars structural stability map gives a clue of a possible high pressure phase transition to a Ni3Sn type structure. The electronic structure calculations were carried out for both the ambient AuCu3 type cubic phase and the expected Ni3Sn type hexagonal high pressure phase. However, the total energy curves of these two structures do not intersect even at pressure as high as 360GPa, removing the possibility of transition to Ni3Sn type structure.

Structural evolution of Lanthanide-based metallic glasses under high pressure annealing

The structural evolutions of Lanthanide-based metallic glasses under high pressure annealing were investigated by using X-ray diffraction, differential scanning calorimetry, in situ high pressure angle dispersive X-ray diffraction measurements with synchrotron radiation, and nanoindentation. The results show that the amorphous structure in the glasses keeps quite stable up to approximately 40GPa at room temperature. The high pressure annealing treatments reveal that pressure can inhibit the crystallization process, improve local packing efficiency, and restrain long-range atom diffusion. The thermal stability and hardness of the alloys both improved after the treatment. The approach has implications for the design of the microstructure- and property-controllable functional materials for various applications.

High pressure investigation of ductile intermetallic HoCu

The results of high-pressure angle dispersive X-ray diffraction measurements up to 27.8 GPa on the ductile intermetallic HoCu is presented. The ambient CsCl structure (SG:Pm-3m) is found to be stable upto the highest pressure of the present measurements. The pressure-volume data fitted to second order Birch-Murnaghan equation of state yields the bulk modulus and its pressure derivative as 76.8 GPa and 4 respectively.

Strength and equation of state of fluorite phase CeO2 under high pressure

Fluorite phase CeO2 is compressed non-hydrostatically up to 27 GPa using a diamond anvil cell until the transition to α-PbCl2 phase occurred. The compressive strength (t) of CeO2 as a function of pressure is determined by the line width analysis of the high pressure angle dispersive x-ray diffraction patterns. The strength of CeO2 increases quickly below 3.30 GPa and reaches a plateau region at high pressures. A procedure combined the line width analysis and the line shift analysis together, based on the non-hydrostatic data to obtain the corresponding lattice parameter under hydrostatic pressures, is proposed and applied to the case of CeO2 sample. The bulk modulus and its pressure derivative of fluorite phase CeO2 (K0 = 235 (18) GPa, K0′ = 3.67) are obtained by fitting the P-V results into Vinet equation of state. A discussion of the pressure dependence of α, which determines the relative weights of the isostress and isostrain conditions across the grain boundary in an actual case, is presented.

High pressure-induced structural phase transition in hexagonal CeF3 nanoplates

The CeF3 nanoplates with hexagonal shape have been successfully synthesized by an ultrasound vibration assisted hydrothermal process. In situ high pressure angle-dispersive synchrotron x-ray diffraction (ADXD) measurements for of CeF3 nanoplates were carried out up to 24 GPa using diamond anvil cell. The ADXD results show that a hexagonal-to-orthorhombic phase transition occurred around 6.8 GPa which is about 13 GPa lower than that reported in bulk CeF3 materials. The bulk modulus (B0) of orthorhombic structure CeF3 nanoplates is close to that of the corresponding bulk. The novel high pressure behaviors of CeF3 nanoplates possibly are due to their unique 2D morphologies.

New high-pressure phase and equation of state of Ce2Zr2O8

In this paper we report a new high-pressure rhombohedral phase of Ce2Zr2O8 observed in high-pressure angle-dispersive x-ray diffraction and Raman spectroscopy studies up to nearly 12 GPa. The ambient-pressure cubic phase of Ce2Zr2O8 transforms to a rhombohedral structure beyond 5 GPa with a feeble distortion in the lattice. The pressure evolution of the unit-cell volume showed a change in compressibility above 5 GPa. The unit-cell parameters of the high-pressure rhombohedral phase at 12.1 GPa are ah = 14.6791(3) Å, ch = 17.9421(5) Å, and V = 3348.1(1) Å3. The structure relations between the parent cubic (P213) and rhombohedral (P32) phases were obtained via group-subgroup relations. All the Raman modes of the cubic phase showed linear evolution with pressure, with the hardest one at 197 cm−1. Some Raman modes of the high-pressure phase have a non-linear evolution with pressure, and softening of one low-frequency mode with pressure is found. The compressibility, equation of state, and pressure coefficients of Raman modes of Ce2Zr2O8 are also reported.

Structural Stability and Compressibility Study for ZnO Nanobelts under High Pressure

The study of nanoscale materials with well-controlled shape could help us to learn more about the morphology effect on phase stability and elastic properties. In situ high-pressure synchrotron angle-dispersive X-ray diffraction for nanobelt and bulk ZnO was measured side-by-side in the same diamond anvil cell at room temperature up to 29 GPa. The pressure-induced wurtzite-type to rocksalt-type structural transition was observed starting at 9.3 GPa for both of these two types of ZnO samples, and no enhanced structural stability for ZnO nanobelts under pressure was found. The relative bigger bulk moduli of wurtzite- and rocksalt-type ZnO nanobelts implicated the morphology effect on its compressibility.

Pressure-Induced Disordered Substitution Alloy in Sb2Te3

A new type of disordered substitution alloy of Sb and Te at above 15.1 GPa was discovered by performing in situ high-pressure angle-dispersive X-ray diffraction experiments on antimony telluride (Sb(2)Te(3)), a topological insulator and thermoelectric material, at room temperature. In this disordered substitution alloy, Sb(2)Te(3) crystallizes into a monoclinic structure with the space group C2/m, which is different from the corresponding high-pressure phase of the similar isostructural compound Bi(2)Te(3). Above 19.8 GPa, Sb(2)Te(3) adopts a body-centered-cubic structure with the disordered atomic array in the crystal lattice. The in situ high-pressure experiments down to about 13 K show that Sb(2)Te(3) undergoes the same phase-transition sequence with increasing pressure at low temperature, with almost the same phase-transition pressures.

Phase transition of cadmium fluoride under high pressure

We investigated the high pressure phases of CdF 2 by a joint theoretical and experimental study. The structural and electronic properties of CdF 2 were extensively explored to high pressure by ab initio calculations based on the density functional theory. A structural phase transition from the fluorite-type ( Fm-3m, Z = 4 ) structure to the cotunnite-type ( Pnma, Z = 4 ) structure was estimated below 8 GPa, and this phase transition was examined by the high pressure experiments up to 35 GPa at room temperature. Both high pressure angle dispersive X-ray diffraction and Raman spectroscopy experiments provided convincing evidence to verify the phase transition. Our work makes clear pressure-induced phase transitions and structural information of CdF 2 under high pressure.

Study on phase transition of SrTiO3 by in situ impedance measurement under high pressure

The pressure dependence of electrical resistance of perovskite SrTiO 3 has been studied by in situ impedance measurement in diamond anvil cell up to 31GPa at room temperature. Two discontinuous changes in resistance were observed at about 9.8 and 21 GPa, which are coincident with the pressure-induced phase transitions from cubic phase to tetragonal phase and then to orthorhombic phase, respectively. High-pressure angle dispersive X-ray diffraction experiments on SrTiO 3 powders have also been performed up to 35 GPa. It was found that a structure phase transition from cubic to tetragonal phase begins to take place at about 6.49 GPa but clear indication for a further transition to an orthorhombic phase at higher pressure up to 35 GPa is hardly seen in our X-ray diffraction data.

High pressure investigation on double perovskite Ba 2MgWO 6

The results of high-pressure angle dispersive X-ray diffraction measurements up to 34.3 GPa on the double perovskite Ba 2MgWO 6 are presented. The ambient rock salt phase ( SG: Fm- 3m) is found to be stable up to the highest pressure of the present measurements. The third order Birch–Murnaghan equation of state when fitted to pressure–volume data, yielded a zero pressure bulk modulus ( B 0),and its first and second pressure derivatives as 137.0(81) GPa, and 3.9(5) and −0.03 GPa −1, respectively.

CORRELATION BETWEEN STRUCTURAL STABILITY AND ELECTRONIC STRUCTURE OF UGa3 UP TO 30 GPa

High-pressure angle-dispersive X-ray diffraction experiments were performed on UGa 3 up to 30 GPa within a diamond-anvil cell. UGa 3 remains in its cubic AuCu 3 type structure up to the maximum pressure studied and does not show any structural phase transition. To understand the structural stability of UGa 3, band structure calculations were performed as a function of reduced volume using the full-potential linear augmented plane wave (FP-LAPW) method. The results show that the Fermi level coincides with a deep valley in the density of states (DOS) curve in the antiferromagnetic state, whereas it lies near a valley (towards the bonding side) in the nonmagnetic state. At high pressures, the DOS near EF does not show much variation in both the cases. The experimental and theoretical equation of state, bulk modulus, and its pressure derivative values are also reported. The pressure dependence of magnetic moment shows a linear decrease at the rate of dμ/dP = -0.027 μ B / GPa .

High-Pressure Irreversible Amorphization of La<sub>1/3</sub>NbO<sub>3</sub>

The crystallographic structure of La1/3NbO3 perovskite was studied at high pressures using a diamond-anvil cell and synchrotron radiation. High-pressure energy dispersive (EDS) x-ray diffraction and high-pressure angle dispersive (ADS) x-ray diffraction revealed an irreversible amorphization at ~10 GPa. A large change in the bulk modulus accompanied the high-pressure amorphization.

Elastic and structural instability of cubicSn3N4andC3N4under pressure

We use in-situ high pressure angle dispersive x-ray diffraction measurements to determine the equation of state of cubic tin nitride Sn3N4 under pressure up to about 26 GPa. While we find no evidence for any structural phase transition, our estimate of the bulk modulus (B) is 145 GPa, much lower than the earlier theoretical estimates and that of other group IV-nitrides. We corroborate and understand these results with complementary first-principles analysis of structural, elastic and vibrational properties of group IV-nitrides, and predict a structural transition of Sn3N4 at a higher pressure of 88 GPa compared to earlier predictions of 40 GPa. Our comparative analysis of cubic nitrides shows that bulk modulus of cubic C3N4 is the highest (379 GPa) while it is structurally unstable and should not exist at ambient conditions.

High-pressure two-dimensional angle-dispersive x-ray diffraction measurement system using a Kawai-type multianvil press at SPring-8

We have demonstrated the feasibility of a two-dimensional angle-dispersive x-ray diffraction (2D-ADXD) measurement system using a Kawai-type multianvil press at SPring-8. By taking advantage of the x-ray-transparent anvil and energy-dispersive x-ray diffraction (EDXD) techniques, high-pressure 2D-ADXD measurements of KCl were performed up to 9.9 GPa. Entire Debye-Scherrer rings were obtained, and the B1-B2 phase change of KCl was clearly observed at 2.3 GPa. The developed 2D-ADXD measurement system enabled us to obtain enough high-quality diffraction data to precisely determine and refine the structure of KCl at high-pressure.

Synchrotron X-ray Diffraction and Infrared Spectroscopy Studies of C60H18 under High Pressure

In situ high-pressure angle-dispersive synchrotron X-ray diffraction and high-pressure mid-infrared (IR) spectrum measurements of C60H18 were carried out up to 32 and 10.2 GPa, respectively. Our diffraction data indicated that the fcc structure of C60H18 was stable up to 32 GPa. The bulk modulus B0 was determined to be 21 ± 1.16 GPa, about 40% higher than that of C60. The C−H vibrations still existed up to 10.2 GPa, and the vibrational frequencies decreased with increasing pressure. IR-active vibrational frequencies and their corresponding eigenvectors of C60H18 were simulated by DMOL3. The effects of the hydrogen atoms attached to the fullerene molecular cage on the stability of the structure under high pressure are discussed.

Phase transition of Zn2SnO4 nanowires under high pressure

In situ high-pressure angle dispersive x-ray diffraction experiments using synchrotron radiation on inverse spinel structure Zn2SnO4 nanowires were carried out with a diamond anvil cell at room temperature. The crystal symmetry becomes lower at around 12.9 GPa and an intermediate phase with an orthorhombic structure occurs. At about 32.7 GPa, a phase transition occurs accompanying a high-pressure phase. In situ Raman scattering investigation was also performed to explore the phase transition. In the pressure range 15.5–32.8 GPa, the intermediate phase is also detected and a high-pressure phase is observed above 32.8 GPa. The high-pressure phase is considered to possess the ambient pressure structure of CaFe2O4.

In situ X-ray diffraction investigation of compression behavior in Gd40Y16Al24Co20 bulk metallic glass under high pressure with synchrotron radiation

The compression behavior of the heavy RE-based BMG Gd40Y16Al24Co20 under high pressure has been investigated by in situ high pressure angle dispersive X-ray diffraction measurements using synchrotron radiation in the pressure range of 0∼33.42 GPa at room temperature. By fitting the static equation of state at room temperature, we find the value of bulk modulus B is 61.27±4 GPa which is in good agreement with the experimental study by pulse-echo techniques of 58 GPa. The results show that the amorphous structure in the heavy RE-based BMG Gd40Y16Al24Co20 keeps quite stable up to 33.42 GPa although its compressibility is as large as about 33%. The coexistence of normal local structure similar to that of other BMGs and covalent bond structure similar to those of oxide glasses may be the reason for the anomalous property under high pressure of the Gd40Y16Al24Co20 BMG.

Pressure tuned crystal structure in NdBa 2Cu 3O 6+δ superconductor

The high-pressure angle-dispersive X-ray diffraction experiments on the NdBa 2Cu 3O 6+ δ superconductor were performed from ambient to above 30 GPa at room temperature. The structure analysis based on the Rietveld refinement methods shows the different pressure dependence for the bond length between the basal-plane copper of the pyramids to the apical oxygen (denoted Cu(2)–O(1)) and bond length between basal-plane copper to plane oxygen (denoted Cu(2)–O(2,3)). The ambient bulk modulus B 0 is derived as 127 GPa. A possible correlation between Cu(2)–O(1) and T c was discussed.