High-pressure X-ray Diffraction Study Research Articles

High-pressure phase transition in Ho2O3

Abstract High-pressure X-ray diffraction and Raman studies on holmium sesquioxide (Ho2O3) have been carried out up to a pressure of ∼17 GPa in a diamond-anvil cell at room temperature. Holmium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase transition at around 9.5 GPa. The high-pressure phase has been identified to be low symmetry monoclinic type. The two phases coexist to up to about 16 GPa, above which the parent phase disappears. The high-pressure laser-Raman studies have revealed that the prominent Raman band ∼370 cm−1 disappears around the similar transition pressure. The bulk modulus of the parent phase is reported.

Unusually large structural stability of terbium oxide phase under high pressure

Abstract High-pressure X-Ray diffraction studies on terbium oxide have been carried out up to a pressure of ∼35 GPa in a diamond anvil cell at room temperature. Terbium oxide, which exhibits the fluorite structure at ambient conditions, remains stable in its fluorite form up to a pressure of ∼27 GPa. Above 27 GPa, it undergoes a structural phase transition accompanied with broadening and appearance of new diffraction peaks. The large structural stability of the compound under pressure is thus unusual when compared with other rare earth sesquioxides, and has been attributed to the presence of Tb4+ ions. The XPS spectra on the sample confirms the presence of Tb4+ ions. The bulk modulus and its pressure derivative of the parent phase are evaluated and reported.

Structural stability and compressibility of group IV transition metals-based bulk metallic glasses under high pressure

High-pressure x-ray diffraction studies have been carried out on the two group IV transition metals-based bulk metallic glasses (BMGs) Zr57Cu15.4Ni12.6Al10Nb5 and Ti42Zr24Cu15.5Ni14.5Be4 to a pressure of 30 GPa at ambient temperature in a diamond anvil cell. Image plate x-ray diffraction studies under high pressure were carried out at a synchrotron source and the two BMG diffraction bands can be followed to the highest pressure using an internal copper pressure standard. The amorphous phase is observed to be stable to the highest static pressure of 30 GPa suggesting that the phase change observed in dynamical pressure experiments is related to an increase in temperature. The measured bulk modulus (B0) and its pressure derivative (B′) are 118 GPa and 3.11 for Zr-based BMG and 116 GPa and 2.84 for Ti-based BMG. The measured bulk modulus for BMG’s by x-ray diffraction technique is consistent with the ultrasonic measurements. The decompression data reveal an increase in density by 3%–4% at ambient condition after pressure cycling to 30 GPa indicating reduction in excess free volume.

High-pressure X-ray diffraction study of ε-FeOOH

An in situ synchrotron X-ray diffraction study was carried out on e-FeOOH at room temperature up to a pressure of 8.6 GPa using the energy-dispersive method. The linear compressibility was determined to be β a = 1.69(3) × 10−3 GPa−1, β b = 2.86(6) × 10−3 GPa−1, and β c = 1.73(5) × 10−3 GPa−1. The b-axis of the unit cell is more compressible than the a and c axes. The pressure–volume data were fitted to a third-order Birch–Murnaghan equation of state. The best fit was found using a room temperature isothermal bulk modulus of K 0 = 126(3) GPa and its pressure derivative K′ = 10(1).

On the structure of high-pressure high-temperature η-O2

In situ high-pressure high-temperature x-ray diffraction and optical studies have been conducted on solid oxygen between 10 and 20 GPa and up to 700 K. Optical observations and Raman spectroscopic studies have been utilized to confirm the existence of eta-O(2) and to identify phase behavior and phase boundaries of beta-, epsilon- and eta-O(2) at elevated temperatures. Subsequent single-crystal synchrotron x-ray diffraction studies yielded the structure of the eta-O(2) phase at 15.9 GPa and 625 K.

High-pressure and high-temperature X-ray diffraction studies of scheelite BaWO4

We carried out high-pressure (HP) and high-temperature (HT) in situ ADXRD synchrotron measurements in barium tungstate (BaWO4) up to 7.5 GPa and 800 K. Coexistence of the scheelite and fergusonite structures was found beyond 7 GPa, both at room temperature and HT, suggesting a polymorphism zone in the P–T phase diagram. The experiments are complemented by thermodynamic calculations within the quasi-harmonic approximation. At ambient pressure, a volume thermal expansivity of 9.5×10−6 K−1 was obtained for scheelite BaWO4. At HP, the thermal expansivity of the fergusonite doubles that of scheelite. Theoretical equation of state curves at HP and HT are also presented.

A high pressure x-ray diffraction study of titanium disulfide

A high pressure angle dispersive synchrotron x-ray diffraction study of titanium disulfide(TiS2)was carried out to pressures of 45.5 GPa in a diamond-anvil cell. We observed a phase transformationof TiS2 beginning at about 20.7 GPa. The structure of the high pressure phaseneeds further identification. By fitting the pressure–volume data to thethird-order Birch–Murnaghan equation of state, the bulk modulus,K0T, was determinedto be 45.9 ± 0.7 GPa with itspressure derivative, K′0T, being 9.5 ± 0.3 at pressures lower than 17.8 GPa. It was found that the compression behavior ofTiS2 is anisotropic along the different axes. The compression ratio of thec-axis is about ninetimes larger than the a-axis when pressures are lower than 1 GPa. It suddenly decreases to three times larger atpressures of about 3 GPa. This ratio shows a linear decrease with a slope of negative 0.048at pressures below phase transformation.

High-pressure x-ray diffraction and Raman spectra study of indium oxide

High-pressure synchrotron radiation x-ray diffraction and Raman spectroscopy measurements of indium oxide (In2O3) were carried out at room temperature up to 27.8 and 26.2 GPa, respectively. A pressure-induced phase transition from cubic-phase (Ia3¯) was observed at a pressure above 12.8–15.3 GPa, which disagrees with earlier theoretical prediction (3.8 GPa). According to the x-ray diffraction experimental data, the high-pressure phase is isostructural with hexagonal corundum-type structure (R3¯c symmetry). However, broad peaks observed in Raman spectra suggest that the high-pressure structure is disordered. The volume change from cubic phase to corundum phase is about 4% and the axial ratio c/a in the corundum phase decreases with increasing pressure.

High-pressure x-ray diffraction study on the structure and phase transitions of the defect-stannite ZnGa2Se4 and defect-chalcopyrite CdGa2S4

X-ray diffraction measurements on the sphalerite-derivatives ZnGa2Se4 and CdGa2S4 have been performed upon compression up to 23 GPa in a diamond-anvil cell. ZnGa2Se4 exhibits a defect tetragonal stannite-type structure (I4¯2m) up to 15.5 GPa and in the range from 15.5 to 18.5 GPa the low-pressure phase coexists with a high-pressure phase, which remains stable up to 23 GPa. In CdGa2S4, we find that the defect tetragonal chalcopyrite-type structure (I4¯) is stable up to 17 GPa. Beyond this pressure a pressure-induced phase transition takes place. In both materials, the high-pressure phase has been characterized as a defect-cubic NaCl-type structure (Fm3¯m). The occurrence of the pressure-induced phase transitions is apparently related with an increase in the cation disorder on the semiconductors investigated. In addition, the results allow the evaluation of the axial compressibility and the determination of the equation of state for each compound. The obtained results are compared to those previously reported for isomorphic digallium sellenides. Finally, a systematic study of the pressure-induced phase transition in 23 different sphalerite-related ABX2 and AB2X4 compounds indicates that the transition pressure increases as the ratio of the cationic radii and anionic radii of the compounds increases.

A diamond anvil cell with resistive heating for high pressure and high temperature x-ray diffraction and absorption studies

In this paper we describe a prototype of a diamond anvil cell (DAC) for high pressure/high temperature studies. This DAC combines the use of a resistive oven of 250 W power in a very small volume, associated with special conical seats for Boehler-type diamond anvils in order to have a large angular acceptance. To protect the diamond anvils from burning and to avoid the oven oxidation, the heated DAC is enclosed in a vacuum chamber. The assemblage was used to study the melting curve of germanium at high pressure (up to 20 GPa) and high temperature (up to 1200 K) using x-ray diffraction and x-ray absorption spectroscopy.

Crystal structure and high-pressure studies of WAl 2, an aluminide crystallizing with the CrSi 2 structure type

The novel intermetallic compound WAl 2 crystallizes with space group P6 422 and lattice parameters a=4.7422(1) Å, c=6.6057(2) Å. The crystal structure was solved from single-crystal X-ray diffraction data. WAl 2 was found to be the first aluminide that is isotypic with CrSi 2. A high-pressure powder X-ray diffraction study showed its stability up to at least 31.5(1) GPa. The bulk modulus was calculated by fitting a third-order Birch–Murnaghan equation of state to the pressure–volume data as K 0=168(11) GPa and its pressure derivative K′=7.7(1.0). Partially covalent bonding between W and Al atoms was indicated by means of the electron localization function (ELF) and explains the anisotropic compression behavior. Quantum chemical calculations identify WAl 2 as a potential high-temperature phase.

Pressure induced structural transformation of pyrochlore Gd 2Zr 2O 7

High pressure x-ray diffraction studies on Gd 2Zr 2O 7 pyrochlore were carried out up to 45 GPa using a diamond anvil cell. A structural transition leading to monoclinic phase is initiated at a very low pressure of ∼3 GPa. Coexistence of both the parent and the daughter phase was seen up to the maximum pressure of 45 GPa. Bulk modulus of the parent phase is found to be 161.5 GPa and the lattice parameters of the high pressure monoclinic phase at 9 GPa are found to be: a=7.4839 Å, b=5.7089 Å, c=12.6498 Å and β = 97.61 . The structural phase transition is found to be reversible when quenched from 10 GPa, but it is irreversible when quenched from 45 GPa. Also, onset of amorphisation is seen above 35 GPa.

High-pressure x-ray diffraction study on lithium borohydride using a synchrotron radiation

Lithium borohydride (LiBH4) was compressed up to 10 GPa using a diamond-anvil-cell to investigate its high-pressure structure. In-situ x-ray diffraction profiles indicated a pressure-induced transformation at 1.1 GPa, which was consistent with the previous experimental observation such as Raman scattering spectroscopy. The high-pressure phase was indexed on a tetragonal symmetry of P42/mmc, which was not corresponding some structural models proposed by previous calculation studies. An unknown substance (presumably another Li-B-H compound), which was contained in the starting material, also transformed into its high-pressure phase at 0.6 GPa without any relation to the transformation of LiBH4.

Monoclinic FeO at high pressures

Abstract A high-pressure quasi-single crystal X-ray diffraction study of a synthetic iron oxide Fe0.95O sample was performed up to 80 GPa using the diamond anvil cell technique. At a pressure of about 75 GPa after laser annealing we observed a new high-pressure monoclinic modification of FeO with P21/m space group. The structure is closely related to that of cubic sodium chloride as a distortion of the lattice. The sequence of transitions cubic-trigonal-monoclinic for FeO follows group-subgroup relations.

Cubic to hexagonal structural transformation in Gd2O3 at high pressure

High-pressure X-ray diffraction studies on gadolinium sesquioxide (Gd2O3) have been carried out up to a pressure of ∼25 GPa in a diamond-anvil cell at room temperature. Gadolinium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase at around 12 GPa. The high-pressure phase has been identified as a hexagonal La2O3-type structure. The bulk modulus and its pressure derivative of this phase have been calculated.

High-pressure structural integrity and structural transformations of glass-derived nanocomposites: A review

A review of our recent and ongoing extensive high-pressure synchrotron X-ray diffraction and high-pressure optical spectroscopy studies of nanocrystalline composites is presented. These heterophased, nano-architectured composites consist of amorphous matrices with dispersed nanocrystals or quantum dots. We show how besides compositional variations, additional tuning of these glass-derived nanocomposites can be done by exploiting elevated pressure. We examine stability and pressure-driven phase transitions occurring in nanocrystals as well as structural changes occurring in the glass matrix. Finally, we discuss the influence of the glass matrix of a composite on the structural transformations occurring in the embedded nanocrystals.

Structural Evolution of BaVS3 Under Pressure

Results of a high-pressure angle dispersive X-ray diffraction and electrical resistance study on quasi one-dimensional BaVS3 are reported. They show that no structural transition occurs up to 26 GPa. However, there is evidence of gradual disordering indicated by the broadening of the diffraction lines. p-V data fitted to a Birch-Murnaghan equation of state yields a value of the room-temperature, ambient-pressure bulk modulus of 77.3 GPa with a pressure derivative of 4.03. It is proposed that under compression structural phase transitions resulting from static displacements of V ions that are observed at low temperature are suppressed. Instead, a partial “polymerization” of V ions that is dynamic in nature and allows enhanced hopping conduction, starts near 3 GPa and saturates above 15 GPa.

High-pressure X-ray diffraction study of tungsten diselenide

Synchrotron X-ray diffraction was used in conjunction with a diamond anvil cell to investigate the properties of a tungsten diselenide (WSe 2) sample to 35.8 GPa at room temperature. By fitting the pressure–volume data to the third-order Birch–Murnaghan equation of state, the bulk modulus, K 0T, of WSe 2 was determined to be 72±1 GPa with its pressure derivative, K 0 T ′ , being 4.1±0.1. It was also found that the c-direction of the hexagonal structure is significantly more compressible than the a-direction. No phase transformation was clearly observed in the pressure range of our measurements.

In situ high-pressure X-ray diffraction study of densification of a molecular chalcogenide glass

Structural mechanisms of densification of a molecular chalcogenide glass of composition Ge 2.5As 51.25S 46.25 have been studied in situ at pressures ranging from 1 atm to 11 GPa at ambient temperature as well as ex situ on a sample quenched from 12 GPa and ambient temperature using high-energy X-ray diffraction. The X-ray structure factors display a reduction in height of the first sharp diffraction peak and a growth of the principal diffraction peak with a concomitant shift to higher Q-values with increasing pressure. At low pressures of at least up to 5 GPa the densification of the structure primarily involves an increase in the packing of the As 4S 3 molecules. At higher pressures the As 4S 3 molecules break up and reconnect to form a high-density network with increased extended-range ordering at the highest pressure of 11 GPa indicating a structural transition. This high-density network structure relaxes only slightly on decompression indicating that the pressure-induced structural changes are quenchable.

X-ray diffraction study of molybdenum diselenide to 35.9 GPa

In situ high-pressure angle dispersive synchrotron X-ray diffraction studies of molybdenum diselenide (MoSe 2) were carried out in a diamond-anvil cell to 35.9 GPa. No evidence of a phase transformation was observed in the pressure range. By fitting the pressure–volume data to the third-order Birch–Murnaghan equation of state, the bulk modulus, K 0T, was determined to be 45.7±0.3 GPa with its pressure derivative, K′ 0T, being 11.6±0.1. It was found that the c-axis decreased linearly with pressure at a slope of −0.1593 when pressures were lower than 10 GPa. It showed different linear decrease with the slope of a −0.0236 at pressures higher than 10 GPa.