High-pressure Structural Behavior Research Articles

Raman spectroscopic insights into the pressure-induced phase transition in natural elbaite

Tourmaline [XY₃Z₆(T₆O₁₈)(BO₃)₃V₃W] is a potential carrier for water and boron cycles in the Earth's interior. Its high-pressure structural behavior has been extensively investigated by single-crystal or powder X-ray diffraction. Here, we collected Raman spectroscopy data of natural elbaite with two different compositions (Fe-poor elbaite and Fe-rich elbaite) up to 35.1 GPa to complementarily characterize the structural modifications proposed by previous studies. Our results reveal two clear discontinuous changes in high-pressure Raman spectra of both samples. The first change occurred at around 15 GPa, characterized by changes in Raman peak intensity, and the pressure dependence of the frequencies of several lattice vibration modes and hydroxyl stretching vibrations. The second change emerged at around 26 GPa and was marked by the systematic appearance of new Raman peaks. Based on previous X-ray diffraction studies, the change at around 26 GPa is likely caused by a phase transition from rhombohedral R3m to rhombohedral R3, whereas the change at around 15 GPa is likely caused by a change in compression mechanism. Furthermore, the WOH stretching vibrations at 3691 cm−1 in Fe-rich elbaite exhibited a negative pressure coefficient, contrasting with the positive pressure coefficient observed in Fe-poor elbaite, suggesting a significant influence of chemical composition on the evolution of stretching vibration in WOH groups under high pressure. After release of pressure, the spectra return to their initial state, indicating the reversibility of all observed changes.

High-pressure structural behavior of α-K2Ca3(CO3)4 up to 20 GPa

High-pressure structural behavior of α-K2Ca3(CO3)4 up to 20 GPa

High-pressure structural behavior and elastic properties of Ce2In and Ce3In: A combined in situ synchrotron X-ray diffraction and density functional theory study

Across the cerium (Ce)-indium (In) binary phase diagram, there are five line compounds including Ce3In, Ce2In, Ce3In5, CeIn2 and CeIn3. So far, CeIn3 is the only compound whose high-pressure structural behavior and elastic properties have been studied in detail. In this work, we investigated the compression behavior of Ce3In and Ce2In at pressures up to 26.2 GPa using in situ high-pressure angle dispersive synchrotron powder X-ray diffraction (XRD). Our results indicate that Ce3In retains its Cu3Au-type structure in the pressure range investigated, whereas Ce2In undergoes a phase transformation from the Ni2In-type structure to an unidentified phase at ∼4.6 GPa. Unit-cell parameters as a function of pressure were obtained by Rietveld analysis of XRD data. Unit cell volumes were fitted to a second order Birch-Murnaghan equation of state (EOS). The experimentally determined bulk moduli (K0) of the two cerium indides are 50 ± 3 GPa for Ce3In and 39.2 ± 1.6 GPa for Ce2In. The zero-pressure compressibilites of the a-axis (βa,0) for Ce3In is 6.67 (±0.36) × 10–3 GPa–1 and of the a- and c-axis for Ce2In are βa,0 = 8.85 (±0.39) × 10−3 GPa−1 and βc,0 = 9.26 (±0.51) × 10−3 GPa−1, respectively. These results are in general agreement with those calculated by density functional theory (DFT + U) and open-source machine learning algorithms.

High-pressure phase of cold-compressed bulk graphite and graphene nanoplatelets

We have studied the high-pressure vibrational and structural behavior of bulk graphite and graphene nanoplatelets at room temperature by means of high-pressure Raman spectroscopic and x-ray diffraction probes. We have detected a clear pressure-induced structural transition in both materials, evidenced by the appearance of new Bragg peaks and Raman features, deviating from the starting hexagonal graphitic structure. The high-pressure phase is identified as a partially disordered orthorhombic structure, consisting of mixed $s{p}^{2}$- and $s{p}^{3}$-type bonding. Our experimental findings serve as direct evidence for the existence of a metastable transient modification in cold compressed carbon, lying between the $s{p}^{2}$-type graphite and ${sp}^{3}$-type diamond allotropes.

Phonon anharmonicity and equation of state parameters of orthovanadate Mg3(VO4)2: Raman Spectroscopy and X-ray diffraction investigation

Isothermal compression effect is investigated on structure and vibrational properties of orthovanadate Mg3(VO4)2 using Raman spectroscopy and X-ray powder diffraction up to pressures 20.2 and 25.7 GPa respectively. Isobaric temperature effect on the vibrational properties of Mg3(VO4)2 have also been investigated using Raman spectroscopy up to 1273 K. The present investigation indicates stable orthorhombic (Cmca) structure up to the highest pressure achieved and up to near its melting temperature. The high pressure structural behavior is similar to the isostructural compounds Zn3(VO4)2 and Ni3(VO4)2 unlike another isostructural compound Mn3(VO4)2 which is reported to show irreversible structural phase transformation. Experimental equation of state parameters are compared with those reported on the similar compounds and the obtained bulk modulus (141 GPa) of Mg3(VO4)2 matches very well with the empirically calculated value reported earlier. The anharmonicities estimated after combining both studies suggest dominant contribution of three phonon decay process.

Comprehensive determination of the high-pressure structural behaviour of BaTiO3

Comprehensive determination of the high-pressure structural behaviour of BaTiO₃

Exploring High-Pressure Transformations in Low-Z (H2, Ne) Hydrates at Low Temperatures

The high pressure structural behavior of H2 and Ne clathrate hydrates with approximate composition H2/Ne·~4H2O and featuring cubic structure II (CS-II) was investigated by neutron powder diffraction using the deuterated analogues at ~95 K. CS-II hydrogen hydrate transforms gradually to isocompositional C1 phase (filled ice II) at around 1.1 GPa but may be metastably retained up to 2.2 GPa. Above 3 GPa a gradual decomposition into C2 phase (H2·H2O, filled ice Ic) and ice VIII’ takes place. Upon heating to 200 K the CS-II to C1 transition completes instantly whereas C1 decomposition appears sluggish also at 200 K. C1 was observed metastably up to 8 GPa. At 95 K C1 and C2 hydrogen hydrate can be retained below 1 GPa and yield ice II and ice Ic, respectively, upon complete release of pressure. In contrast, CS-II neon hydrate undergoes pressure-induced amorphization at 1.9 GPa, thus following the general trend for noble gas clathrate hydrates. Upon heating to 200 K amorphous Ne hydrate crystallizes as a mixture of previously unreported C2 hydrate and ice VIII’.

Unconventional iron-magnesium compounds at terapascal pressures

Being a lithophile element at ambient pressure, magnesium is long believed to be immiscible with iron. A recent study by Gao et al. [1] showed that pressure turns magnesium into a siderophile element and can produce unconventional Fe-Mg compounds. Here, we extend the investigation to exoplanetary pressure conditions using an adaptive genetic algorithm-based variable-composition structural prediction approach. We identify several Fe-Mg phases up to 3 TPa. Our cluster alignment analysis reveals that most of the predicted Fe-Mg compounds prefer a BCC packing motif at terapascal pressures. This study provides a more comprehensive structure database to support future investigations of the high-pressure structural behavior of Fe-Mg and ternary, quaternary, etc. compounds involving these elements.

High-pressure behavior of disordered kesterite-type Cu2ZnSnS4

We have investigated the high-pressure structural and vibrational behavior of the disordered kesterite-type Cu2ZnSnS4 compound at ambient temperature. Our experimental and theoretical investigations have revealed a clear structural transition to a GeSb-type phase close to 15 GPa, a tetragonally distorted variant of the NaCl-type phase. The latter transformation is accompanied by a cationic coordination increase from fourfold to sixfold with respect to the sulfur anions. In addition, a change in the compressibility rate was detected at about 8 GPa within the pressure stability range of the disordered kesterite-type phase. Upon decompression, a disordered zinc blende/sphalerite structure is recovered. We discuss our findings in close conjunction with our recent high-pressure work on the ordered Cu2ZnSnS4 modification.

High-pressure monoclinic–monoclinic transition in fergusonite-type HoNbO4

In this paper we perform a high-pressure (HP) study of fergusonite-type HoNbO4. Powder x-ray diffraction experiments and ab initio density-functional theory (DFT) simulations provide evidence of a phase transition at 18.9(1.1) GPa from the monoclinic fergusonite-type structure (space group I2/a) to another monoclinic polymorph described by space group P21/c. The phase transition is reversible and the HP structural behavior is different than the one previously observed in related niobates. The HP phase remains stable up to 29 GPa. The observed transition involves a change in the Nb coordination number from 4 to 6, and it is driven by mechanical instabilities. We have determined the pressure dependence of unit-cell parameters of both phases and calculated their room-temperature equation of state. For the fergusonite-phase we have also obtained the isothermal compressibility tensor. In addition to the HP studies, we report ambient-pressure Raman and infrared (IR) spectroscopy measurements. We have been able to identify all the active modes of fergusonite-type HoNbO4, which have been assigned based upon DFT calculations. These simulations also provide the elastic constants of the different structures and the pressure dependence of the Raman and IR modes of the two phases of HoNbO4. According to ab initio calculations, the reported phase transition is related to a mechanical instability and a phonon softening.

Comprehensive determination of the high-pressure structural behaviour of BaTiO3

We have mapped the phase diagram of BaTiO3 more extensively than previous attempts using high-pressure neutron-powder diffraction.

High-Pressure Structural Behavior and Equation of State of Kagome Staircase Compound, Ni3V2O8

We report on high-pressure synchrotron X-ray diffraction measurements on Ni3V2O8 at room-temperature up to 23 GPa. According to this study, the ambient-pressure orthorhombic structure remains stable up to the highest pressure reached in the experiments. We have also obtained the pressure dependence of the unit-cell parameters, which reveals an anisotropic compression behavior. In addition, a room-temperature pressure–volume third-order Birch–Murnaghan equation of state has been obtained with parameters: V0 = 555.7(2) Å3, K0 = 139(3) GPa, and K0′ = 4.4(3). According to this result, Ni3V2O8 is the least compressible kagome-type vanadate. The changes of the crystal structure under compression have been related to the presence of a chain of edge-sharing NiO6 octahedral units forming kagome staircases interconnected by VO4 rigid tetrahedral units. The reported results are discussed in comparison with high-pressure X-ray diffraction results from isostructural Zn3V2O8 and density-functional theory calculations on several isostructural vanadates.

Analysis of structural phase stability and thermo-elastic properties of alloy of rare earth sulfides (LaxPr1-xS) under high pressure at room temperature

The high pressure structural behavior and associated properties of mixed rare earth sulfides (LaxPr1-xS) have been investigated by applying a Realistic Interaction Potential (RIP) model, including temperature effects. This model explains the inter-atomic interactions as it incorporates long range coulomb interaction; three body interaction (TBI), vdW (van der Waals) interaction, short range overlap repulsive interaction up to second neighbors and zero point energy effects including the temperature effects. We have predicted the high pressure structural phase transition from NaCl (B1 -type) to CsCl-type (B2-type) phase and associated volume drops for these compounds. The pressure induced phase transition is found to be a first order. Estimation of the elastic, thermal properties and Every’s parameters of these compounds has been performed during study. The results obtained are found to be in reasonable agreement with experimental and other theoretical data.

Effect of cationic substitution on the pressure-induced phase transitions in calcium carbonate

Abstract The high-pressure CaCO3 phase diagram has been the most extensively studied within the carbonates group. However, both the diverse mineralogy of carbonates and the abundance of solid solutions in natural samples require the investigation of multi-component systems at high pressures (P) and temperatures (T). Here we studied a member of the CaCO3–SrCO3 solid-solution series and revealed the effect of cationic substitution on the pressure-induced phase transitions in calcium carbonate. A synthetic solid solution Ca0.82Sr0.18CO3 was studied in situ by Raman spectroscopy in a diamond-anvil cell (DAC) up to 55 GPa and 800 K. The results of this work show significant differences in the high-pressure structural and vibrational behavior of the (Ca,Sr)CO3 solid solution compared to that of pure CaCO3. The monoclinic CaCO3-II-type structure (Sr-calcite-II) was observed already at ambient conditions instead of the “expected” rhombohedral calcite. The stress-induced phase transition to a new high-pressure modification, termed here as Sr-calcite-IIIc, was detected at 7 GPa. Sr-calcite-VII formed already at 16 GPa and room T, which is 14 GPa lower compared to CaCO3-VII. Finally, crystallization of Sr-aragonite was detected at 540 K and 9 GPa, at 200 K lower T than pure aragonite. Our results indicate that substitution of Ca2+ by bigger cations, such as Sr2+, in CaCO3 structures can stabilize phases with larger cation coordination sites (e.g., aragonite, CaCO3-VII, and post-aragonite) at lower P-T conditions compared to pure CaCO3. The present study shows that the role of cationic composition in the phase behavior of carbonates at high pressures should be carefully considered when modeling the deep carbon cycle and mantle processes involving carbonates, such as metasomatism, deep mantle melting, and diamond formation.

High-enthalpy crystalline phases of cadmium telluride

The authors investigate the high-pressure structural behavior of CdTe and characterize the crystal structure of the post-Cmcm phase. The paper finds that above 34 GPa the enthalpy of CdTe is constantly higher than the enthalpy sum of Cd and Te. This indicates that CdTe is a high-enthalpy compound which is stabilized by a large kinetic barrier.

High-pressure structural behavior and elastic properties of U3Si5: A combined synchrotron XRD and DFT study

We present an integrated experimental and theoretical study of the structural behavior of U3Si5 at high-pressure conditions using angle-dispersive synchrotron X-ray diffraction (XRD) in a diamond anvil cell (DAC) and density functional theory (DFT) calculations. On increasing pressure, the ambient hexagonal structure of U3Si5 with space group P6/mmm remains stable up to 16.7 GPa, the maximum pressure tested with DAC. The bulk modulus and the a- and c-axial moduli of U3Si5 were experimentally determined to be 126 ± 4 GPa, 173 ± 8 GPa and 79.7 ± 4.3 GPa, respectively. Thus an anisotropy in the axial compressibility of U3Si5 is observed with its c-axis being more compressible than the a-axis. Our DFT calculation results are in general agreement with the experimental values, including reproducing the compressibility anisotropy. A comparison of the bulk modulus of U3Si5 to those of other U–Si compounds reveals a general trend that the bulk modulus of U–Si decreases with increasing U/(U + Si) ratio.

Comparative study of the high-pressure behavior of ZnV2O6, Zn2V2O7, and Zn3V2O8

Abstract We report a study of the high-pressure structural behavior of ZnV2O6, Zn2V2O7, and Zn3V2O8, which has been explored by means of synchrotron powder x-ray diffraction. We found that ZnV2O6 and Zn3V2O8 remain in the ambient-pressure structure up to 15 GPa. In contrast, in the same pressure range, Zn2V2O7 undergoes three phase transitions at 0.7, 3.0, and 10.8 GPa, respectively. Possible crystal structures for the first and second high-pressure phases are proposed. Reasons for the distinctive behavior of Zn2V2O7 are discussed. The compressibility of the different polymorphs has been determined. The response to pressure is found to be anisotropic in all the considered compounds and the room-temperature equations of state have been determined. The bulk moduli of ZnV2O6 (129(2) GPa) and Zn3V2O8 (120(2) GPa) are consistent with a structural framework composed of compressible ZnO6 octahedra and uncompressible VO4 tetrahedra. In contrast, Zn2V2O7 is highly compressible with a bulk modulus of 58(9) GPa, which is almost half of the bulk modulus of the other two vanadates. The large compressibility of Zn2V2O7 and its sequence of structural transitions are related to the fact that this material is less dense than the other zinc vanadates and to the penta-coordination of Zn atoms by oxygen atoms in Zn2V2O7. A comparison to the high-pressure behavior of related compounds is presented.

High pressure structural behaviour of 5,5'-bitetrazole-1,1'-diolate based energetic materials: a comparative study from first principles calculations.

Pressure on the scale of gigapascals can cause incredible variations in the physicochemical and detonation characteristics of energetic materials. As a continuation of our earlier work (B. Moses Abraham, et al., Phys. Chem. Chem. Phys., 2018, 20, 29693–29707), here we report the high pressure structural and vibrational properties of 5,5′-bitetrazole-1,1′-diolate based energetic ionic salts via dispersion-corrected density functional theory calculations. Remarkably, these energetic materials exhibit anisotropic behavior along three crystallographic directions with progressing pressure; especially, the maximum and minimum reduction in volume is observed for HA-BTO and TKX-50, respectively. The large bulk modulus of TKX-50 (28.64) indicates its hard nature when compared to other BTO-based energetic salts. The effect of pressure on hydrogen bonded D–H⋯A energetic materials induces spectral shift (lengthening/shortening) in the donor group (D–H) of the stretching vibrations and is widely recognized as the signature of hydrogen bonding. We observed unusual contraction of the D–H bond under compression due to the short range repulsive forces encountered by the H atom while the molecule attempts to stabilize. The Hirshfeld surface analysis highlights the pressure induced stabilization of HA-BTO due to increased N⋯H/H⋯N and O⋯H/H⋯O close contact of hydrogen bond acceptors and donors. These studies provide theoretical guidance as a function of pressure, on how the micro-structures and intermolecular interactions can tune macroscopic properties to enhance the energetic performance.

High-Pressure Phase Transitions of Morphologically Distinct Zn2SnO4 Nanostructures.

Many aspects of nanostructured materials at high pressures are still unexplored. We present here, high-pressure structural behavior of two Zn2SnO4 nanomaterials with inverse spinel type, one a particle with size of ∼7 nm [zero dimensional (0-D)] and the other with a chain-like [one dimensional (1-D)] morphology. We performed in situ micro-Raman and synchrotron X-ray diffraction measurements and observed that the cation disordering of the 0-D nanoparticle is preserved up to ∼40 GPa, suppressing the reported martensitic phase transformation. On the other hand, an irreversible phase transition is observed from the 1-D nanomaterial into a new and dense high-pressure orthorhombic CaFe2O4-type structure at ∼40 GPa. The pressure-treated 0-D and 1-D nanomaterials have distinct diffuse reflectance and emission properties. In particular, a heterojunction between the inverse spinel and quenchable orthorhombic phases allows the use of 1-D Zn2SnO4 nanomaterials as efficient photocatalysts as shown by the degradation of the textile pollutant methylene blue.

Bulk moduli and high pressure crystal structure of U3Si2

Bulk moduli are important parameters to assess the mechanical performance of materials including nuclear fuels. However, little experimental data exist for U3Si2, a potential accident-tolerant nuclear fuel, whose bulk modulus has only been measured by resonant ultrasonic spectroscopy (RUS). In addition, the knowledge for high-pressure structural behavior and phase equilibrium of U3Si2 is largely lacking. Here we studied pressure dependence of the crystal structure of U3Si2 using high-energy synchrotron X-ray diffraction coupled with Rietveld analysis. The pressurization was achieved using a diamond anvil cell (DAC) which provides quasi-hydrostatic pressures up to 37.6 GPa. Crystal structural variation and equations of state of U3Si2 were obtained, and its bulk modulus, a- and c-axial moduli were derived to be 107.11 ± 5.65 GPa, 82.87 ± 4.78 GPa and 194.52 ± 12.03 GPa, respectively. The determined elastic parameters are compared with those obtained by RUS and nanoindentation.