Murnaghan Equation Research Articles

High-pressure crystal structure and equation of state of ferromagnesian jeffbenite: implications for stability in the transition zone and uppermost lower mantle

Jeffbenite, ideally Mg3Al2Si3O12, has been identified as inclusions in super-deep diamonds originating from depths that exceed 300 km. Although Mg-end member jeffbenite has limited stability at upper-mantle conditions, iron-bearing jeffbenite may have broader P–T stability that extends to the transition zone or uppermost lower mantle, incorporating significant amounts of ferric iron. Using synchrotron-based, single-crystal X-ray diffraction (XRD) and synchrotron Mössbauer spectroscopy (SMS) at pressures up to 29 GPa, we report the crystal structure, compressibility, and likely spin transition of iron in ferromagnesian jeffbenite (Mg2.32Al0.03Fe2+1.28Fe3+1.77Si2.85O12). High-pressure structure refinements reveal that Fe3+ substitution for Si in the T2 site, which shares edges with the M2 octahedron, likely stabilizes jeffbenite at high pressure, because it increases the cation-to-cation distance between these sites. Although ferromagnesian jeffbenite does not undergo a structural phase transition below 30 GPa, SMS hyperfine parameters suggest the onset of an electronic spin transition of iron from high-spin (HS) to low-spin (LS) at around 22 GPa, which may increase its stability at high pressures. Pressure–volume data were fit to a third order Birch–Murnaghan equation of state, resulting in V0 = 816.54(9), KT0 = 181.54(1.39), and $${K}_{T0}^{\prime}$$ = 2.76(14). These equation of state parameters are applicable to evaluating the encapsulation pressures of super-deep diamonds. The density and bulk modulus of ferromagnesian jeffbenite are similar to or higher than pyrope–almandine, pyrope–majorite, and skiagite–majorite solid solution garnets, further suggesting that jeffbenite may be an important ferric–iron silicate in the deeper parts of the mantle transition zone and uppermost lower mantle. However, future studies on the influence of temperature and oxidation state on the stability and equations of state of iron-bearing jeffbennite are still needed to determine what role, if any, jeffbenite plays in transition-zone mineralogy.

Thermoelastic parameters of Mg-sursassite and its relevance as a water carrier in subducting slabs

Abstract We report the synthesis, at 7 GPa and 923 K, and the thermoelastic characterization, up to 16 GPa and 850 K, of a single crystal of Mg-sursassite, Mg5Al5Si6O21(OH)7. In situ high-pressure and high-temperature single-crystal diffraction allowed the study of structural variation at non-ambient conditions and the determination of bulk elastic properties. The refined parameters of a second-order Birch-Murnaghan equation of state (BM-II EoS) are V0 = 446.02(1) Å3 and KT0 = 135.6(7) GPa. The thermal expansion coefficients of a Berman-type EoS are α0 = 3.14 (5) × 10−5 K−1, α1 = 2.50(16) × 10−8 K−2, and V0 = 445.94(3). For comparison, the P-V EoS is determined for a natural sursassite sample, ideally Mn4Al6Si6O22(OH)6. The refined parameters of BM-II EoS [V0 = 470.2(3) Å3, KT0 = 128(4) GPa] indicate that composition has a minimal effect on elastic properties. The similarity of density and bulk properties of Mg-sursassite if compared to olivine and other anhydrous mantle minerals suggests that this phase could be overseen by geophysical methods.

Stability and Thermoelasticity of Diaspore by Synchrotron X-ray Diffraction and Raman Spectroscopy

The thermoelasticity and stability of diaspore (α-AlOOH, Al1.002Fe0.003OOH) were investigated in this study by in situ synchronous X-ray diffraction (XRD) and Raman spectroscopy methods at high pressure and high temperature conditions. The results indicate that diaspore is stable within the pressure and temperature (P-T) region examined in this study. With increasing pressure, the Raman peaks move toward the high wave number direction, the intensity of the Raman peaks increases, and the vibration mode of diaspore changes linearly. Pressure-volume data from in situ high-pressure XRD experiments were fitted by the third-order Birch-Murnaghan equation of state (EoS) with the zero-pressure unit-cell volume V0 = 118.15 (4) Å3, the zero-pressure bulk modulus KV0 = 153 (2) GPa, and its pressure derivative K'V0 = 2.4 (3). When K'V0 was fixed at 4, the obtained KV0 = 143 (1) GPa. The axial compressional behavior of diaspore was also fitted with a linearized third-order Birch-Murnaghan EoS, showing slight compression anisotropy with Ka0 = 137 (5) GPa, Kb0 = 169 (7) GPa and Kc0 = 178 (6) GPa. In addition, the temperature-volume data from in situ high-temperature XRD experiments were fitted by Fei’s thermal equation with the thermal expansion coefficients αV = 2.7 (2) × 10–5 K−1, αa = 1.13 (9) × 10–5 K−1, αb = 0.77 (5) × 10–5 K−1, and αc = 0.85 (9) × 10–5 K−1 for diaspore, which shows that diaspore exhibits slightly anisotropic thermal expansion. Furthermore, in situ synchrotron-based single-crystal XRD under simultaneously high P-T conditions indicates that the P-T stability of diaspore is up to ∼10.9 GPa and 700 K. Combined with previous results, we infer that diaspore can be subducted to ∼390 km under cold subduction conditions based on existing experimental data and is a good candidate for transporting water to the deep Earth.

Thermostructural and Elastic Properties of PbTe and Pb0.884Cd0.116Te: A Combined Low-Temperature and High-Pressure X-ray Diffraction Study of Cd-Substitution Effects

Rocksalt-type (Pb,Cd)Te belongs to IV–VI semiconductors exhibiting thermoelectric properties. With the aim of understanding of the influence of Cd substitution in PbTe on thermostructural and elastic properties, we studied PbTe and Pb0.884Cd0.116Te (i) at low temperatures (15 to 300 K) and (ii) at high pressures within the stability range of NaCl-type PbTe (up to 4.5 GPa). For crystal structure studies, powder and single crystal X-ray diffraction methods were used. Modeling of the data included the second-order Grüneisen approximation of the unit-cell-volume variation, V(T), the Debye expression describing the mean square atomic displacements (MSDs), <u2>(T), and Birch–Murnaghan equation of state (BMEOS). The fitting of the temperature-dependent diffraction data provided model variations of lattice parameter, the thermal expansion coefficient, and MSDs with temperature. A comparison of the MSD runs simulated for the PbTe and mixed (Pb,Cd)Te crystal leads to the confirmation of recent findings that the cation displacements are little affected by Cd substitution at the Pb site; whereas the Te displacements are markedly higher for the mixed crystal. Moreover, information about static disorder caused by Cd substitution is obtained. The calculations provided two independent ways to determine the values of the overall Debye temperature, θD. The resulting values differ only marginally, by no more than 1 K for PbTe and 7 K for Pb0.884Cd0.116Te crystals. The θD values for the cationic and anionic sublattices were determined. The Grüneisen parameter is found to be nearly independent of temperature. The variations of unit-cell size with rising pressure (the NaCl structure of Pb0.884Cd0.116Te sample was conserved), modeled with the BMEOS, provided the dependencies of the bulk modulus, K, on pressure for both crystals. The K0 value is 45.6(2.5) GPa for PbTe, whereas that for Pb0.884Cd0.116Te is significantly reduced, 33.5(2.8) GPa, showing that the lattice with fractional Cd substitution is less stiff than that of pure PbTe. The obtained experimental values of θD and K0 for Pb0.884Cd0.116Te are in line with the trends described in recently reported theoretical study for (Pb,Cd)Te mixed crystals.

CoSO4·H2O and its continuous transition compared to the compression properties of isostructural kieserite-type polymorphs

Abstract The kieserite-type compound cobalt(II) sulfate monohydrate, CoSO4·H2O, has been investigated under isothermal (T = 295 K) hydrostatic compression up to 10.1 GPa in a diamond anvil cell by means of single-crystal X-ray diffraction and Raman spectroscopy. The monoclinic α-phase (space group C2/c) undergoes a second-order ferroelastic phase transition at P c = 2.40(3) GPa to a triclinic β-phase (space group P 1 ‾ $‾{1}$ ). Lattice elasticities derived from fitting third-order Birch-Murnaghan equations of state to the pressure dependent unit-cell volume data yield V 0 = 354.20(6) Å3, K 0 = 53.0(1.7) GPa, K′ = 5.7(1.8) for the α-phase and V 0 = 355.9(8) Å3, K 0 = 45.2(2.6) GPa, K′ = 6.6(6) for the β-phase. Crystal structure data of the high-pressure polymorph were determined at 2.98(6) and 4.88(6) GPa. The most obvious structural feature and thus a possible driving mechanism of the phase transition, is a partial rearrangement in the hydrogen bonding system. However, a comparative analysis of pressure-induced changes in the four kieserite-type compounds investigated to date suggests that the loss of the point symmetry 2 at the otherwise rather rigid SO4 tetrahedron, allowing symmetrically unrestricted tetrahedral rotations and edge tiltings in the β-phase, could be the actual driving mechanism of the phase transition.

CsIBr2 at high pressures: An insitu Raman and ADXRD investigation

We report the results of ambient temperature high pressure Raman and synchrotron based ADXRD study of CsIBr2 up to 32 and 25 ​GPa respectively. Raman spectroscopic measurements indicate two phase transitions above 5 and 19 ​GPa respectively. High pressure ADXRD measurements reveal that the ambient orthorhombic (SG:Pnma) phase of CsIBr2 is stable up to a pressure of 5 ​GPa above which a phase transition to a trigonal (SG:P-3c1) phase, coexisting with the ambient phase, is observed. The stability region of the trigonal phase has been found to be up to 19.4 ​GPa above which another phase transition is observed. A third order and second order Birch-Murnaghan equation of state fit to pressure dependence of unit cell volume yielded a bulk modulus of 10.9(8) GPa and 17.8(1) GPa for the orthorhombic and trigonal phase respectively.

High Pressure Behavior of Mascagnite from Single Crystal Synchrotron X-ray Diffraction Data

High-pressure synchrotron X-ray diffraction was carried out on a single crystal of mascagnite, compressed in a diamond anvil cell. The sample maintained its crystal structure up to ~18 GPa. The volume–pressure data were fitted by a third-order Birch–Murnaghan equation of state (BM3-EOS) yielding K0 = 20.4(7) GPa, K’0 = 6.1(2), and V0 = 499(1) Å3, as suggested by the F-f plot. The axial compressibilities, calculated with BM3-EOS, were K0a = 35(3), K’0a = 7.7(7), K0b = 10(3), K’0b = 7(1), K0c = 25(1), and K’0c = 4.3(2) The axial moduli measured using a BM2-EOS and fixing K’0 equal to 4, were K0a = 52(2), K0b = 20 (1), and K0c = 29.6(4) GPa, and the anisotropic ratio of K0a:K0b:K0c = 1:0.4:0.5. The evolution of crystal lattice and geometrical parameters indicated no phase transition until 17.6 GPa. Sulphate polyhedra were incompressible and the density increase of 30% compared to investigated pressure should be attributed to the reduction of weaker hydrogen bonds. In contrast, some of them, directed along [100], were very short at room temperature, below 2 Å, and showed a very low compressibility. This configuration explains the anisotropic compressional behavior and the lowest compressibility of the a axis.

Ab-initio study on physical properties of intermetallic LiPb compound

In our work, some theoretical calculations of LiPb compound in B2 structure have been analyzed using Vienna ab initio simulation package (VASP). The ground state properties are revealed by fitting the calculated total energy-atomic volume to the Murnaghan equation. The studied compound is stable both thermodynamically and dynamically due to the formation of energy and its positive vibration frequencies. This compound shows ductile and soft property from calculated second-order elastic constants. By evaluating the electronic properties, the absence of band gap highlighted the metallic property of the compound. Finally the effects of pressure and temperature on thermodynamic properties were explained in detail.

Compressibility and blue-shifting O–H stretching bands of magnesium hydroxyfluoride Mg(OH)F up to 20 ​GPa

In-situ high-pressure synchrotron X-ray diffraction (XRD) and Fourier transform infrared absorption spectroscopy (FTIR) measurements have been conducted up to ~20 ​GPa at room temperature using diamond anvil cells (DAC), to investigate compressibility and spectroscopic properties of magnesium hydroxyfluoride, Mg(OH)F (Pnma, Z ​= ​4). Without any phase transition being observed, the pressure-volume correlation is fitted by the second-order Birch-Murnaghan equation of state, yielding K0 ​= ​80 (±2) GPa, K0′ ​= ​4.0 (fixed), and V0 ​= ​145.2 (±0.3) Å3. In accordance with other isostructural compounds crystallizing in the diaspore-type structure, higher contraction occurs along the c axis of Mg(OH)F. Positive pressure dependence of the O–H stretching mode frequencies initially observed at 3537 (1.56 ​cm−1/GPa), 3641 (0.67 ​cm−1/GPa), and 3680 ​cm−1 (2.85 ​cm−1/GPa) at ambient pressure indicates that the O–H⋯F hydrogen bond does not strengthen under compression.

Calculating detonation performance of explosives by VLWR thermodynamics code introduced with universal VINET equation of state

Thermodynamic calculation is the theoretical basis for the study of initiation and detonation, as well as the prerequisite for forecasting the detonation performance of unknown explosives. Based on the VLWR(Virial-Wu) thermodynamic code, this paper introduced the universal solid equation of state (EOS) VINET. In order to truly reflect the compressibility of nanocarbon under the extremely high-temperature and high-pressure environment in detonation, an SVM (support vector machine) was utilized to optimize the input parameters of carbon. The detonation performance of several explosives with different densities was calculated by the optimized universal EOS, and the results show that the thermodynamic code coupled with the universal solid EOS VINET can predict the detonation performance parameters of explosives well. To investigate the application of the thermodynamic code with the improved VINET EOS in the working capacity of explosives, the interrelationship between pressure P-particle velocity u and pressure P-volume V were computed for the detonation products of TNT and HMX-based PBX (HMX: binder: insensitive agent = 95:4.3:0.7) in the CJ isentropic state. A universal curve proposed by Cooper was used to compared the computed isentropic state, where the ratio of pressure to CJ state were plotted against the ratio of velocity to CJ state. The parameters of the JWL(Jones-Wilkins-Lee) EOS for detonation products were obtained by fitting the P–V curve. The cylinder tests of TNT and HMX-based PBX were numerically simulated using the LS-DYNA, it is verified that, within a certain range, the improved algorithm has superiority in describing the working capacity of explosives.

Phase transitions of ScOOH under high pressure

ABSTRACT In-situ X-ray diffraction measurements of ScOOH were conducted under high pressure and temperature conditions up to 11 GPa and 900 K to understand its phase transitions. As the pressure increased, α-ScOOH, InOOH-type ScOOH, and YbOOH-type ScOOH were observed. The experimental results indicate that the boundaries between α-ScOOH and InOOH-type ScOOH, and between InOOH-type and YbOOH-type ScOOH are represented by the following linear equations: P(GPa) = (0.0009 ± 0.0015) × [T(K) – 700] + 4.33 ± 0.04 and P(GPa) = (–0.0029 ± 0.0002) × [T(K) – 800] + 8.1 ± 0.3, respectively. By using a least-squares fit of the second-order Birch–Murnaghan equation of state (EoS) to the experimental compression data, the EoS parameters of the three phases of ScOOH at 400 K were obtained. The volume change of the transition from α-ScOOH to InOOH-type ScOOH is ∼3.9% at 4 GPa and 400 K, while the volume change of the transition from InOOH-type to YbOOH-type ScOOH is ∼7.6% at 9 GPa and 400 K.

Equations of state of new boron-rich selenides B6Se and B12Se

ABSTRACT Two novels boron-rich selenides, orthorhombic B6Se and rhombohedral B12Se, have been recently synthesized at high pressures and high temperatures. Room-temperature compressibilities of these phases were studied in a diamond anvil cell using synchrotron powder X-ray diffraction. A fit of experimental p–V data by the third-order Birch–Murnaghan equation of state yielded the bulk moduli of 155(2) GPa for B12Se and 144(3) GPa for B6Se. No pressure-induced phase transitions have been observed in the studied pressure range, that is, up to 35 GPa.

A novel dynamic cavity expansion model to predict the resistance of reactive powder concrete (RPC) against projectile impact

The dynamic cavity expansion (DCE) model is a commonly used analytical model to predict the resistance of concrete materials subjected to projectile impact. In this paper, a modified Griffith strength criterion was proposed for reactive powder concrete (RPC), which has a form easy to solve and can well capture the tensile, compressive and triaxial strength of RPC. Combined with the Murnaghan equation of state, the proposed strength criterion was used as the material model for RPC. The cavity expansion resistance was calculated numerically and analytically. It indicates that the numerical and analytical solutions are almost consistent under the same material response. Then, the strain softening behavior that cannot be resolved analytically was further introduced into the material model, and the numerical solution of the DCE model was obtained using LS-DYNA. To verify the present method, the 122.6 MPa RPC targets were tested using 14.5 mm diameter ogival nose projectiles at impact velocities of from 286 to 942 m/s. Combined with previous penetration model, the penetration depth of the present test was predicted. In addition, numerical simulation of this penetration test adopting the HJC model was also performed. It shows predictions of the present model are in good agreement with test and simulation results. Furthermore, the present model was used to predict the existing test date of RPCs with compressive strength of between 67.5 and 140 MPa, and the effectiveness of the present method was verified by comparing with predictions of previous empirical formulas.

High-pressure behavior of heteroepitaxial core–shell particles made of Prussian blue analogs

We report the compressibility of two Prussian blue analogs (PBAs) under hydrostatic pressure, one with small and one with a relatively large cubic unit cell among PBAs, and investigate the modification of their elastic properties when the two lattices are coupled within a heteroepitaxial core–shell structure. Bulk modulus (K0) values are derived from x-ray powder diffraction experiments using a diamond anvil cell with silicone oil as a pressure-transmitting medium. The pressure–volume curves fitted to Murnaghan equations of states show that K0 inversely scales with the crystal packing for the rubidium cobalt hexacyanoferrate and rubidium nickel hexacyanochromate samples (K0 ∼ 29 GPa for Co-Fe PBA, a0 = 9.95 Å and ∼20 GPa for Ni-Cr PBA, a0 = 10.48 Å with a0 being the lattice constant at ambient pressure). The two single-phase samples undergo a cubic-to-rhombohedral phase transition above ∼0.8 GPa, which correlates fairly well with the build-up of nonhydrostatic pressure contributions in the cell. Within the core–shell structure, the volume change observed for the core scales with that of the shell because of the configuration close to the case of a solid pressure-transmitting medium. The Ni-Cr PBA shell layer exhibits an increased rhombohedral distortion with respect to the single-phase reference possibly associated with shearing at the core–shell interface. Its bulk modulus is not significantly modified with respect to that of the single-phase sample despite the presence of defects associated with the growth mode, whereas the P-V curve of the core suggests a stiffening of the Co-Fe PBA lattice.

High-Pressure Raman Spectroscopy and X-ray Diffraction Study on Scottyite, BaCu2Si2O7

In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic experiments of scottyite, BaCu2Si2O7, were carried out in a diamond anvil cell up to 21 GPa at room temperature. X-ray diffraction patterns reveal four new peaks near 3.5, 3.1, 2.6 and 2.2 Å above 8 GPa, while some peaks of the original phase disappear above 10 GPa. In the Raman experiment, we observed two discontinuities in dν/dP, the slopes of Raman wavenumber (ν) of some vibration modes versus pressure (P), at approximately 8 and 12 GPa, indicating that the Si-O symmetrical and asymmetrical vibration modes change with pressure. Fitting the compression data to Birch–Murnaghan equation yields a bulk modulus of 102 ± 5 GPa for scottyite, assuming Ko′ is four. Scottyite shows anisotropic compressibility along three crystallographic axes, among which c-axis was the most compressible axis, b-axis was the last and a-axis was similar to the c-axis on the compression. Both X-ray and Raman spectroscopic data provide evidences that scottyite undergoes a reversible phase transformation at 8 GPa.

Compressibility and Phase Stability of Iron-Rich Ankerite

The structure of the naturally occurring, iron-rich mineral Ca1.08(6)Mg0.24(2)Fe0.64(4)Mn0.04(1)(CO3)2 ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch–Murnaghan equation of state yields V0 = 328.2(3) Å3, bulk modulus B0 = 89(4) GPa, and its first-pressure derivative B’0 = 5.3(8)—values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO3)2 ankerite composition. At 12 GPa, the iron-rich ankerite structure undergoes a reversible phase transition that could be a consequence of increasingly non-hydrostatic conditions above 10 GPa. The high-pressure phase could not be characterized. DFT calculations were used to explore the relative stability of several potential high-pressure phases (dolomite-II-, dolomite-III- and dolomite-V-type structures), and suggest that the dolomite-V phase is the thermodynamically stable phase above 5 GPa. A novel high-pressure polymorph more stable than the dolomite-III-type phase for ideal CaFe(CO3)2 ankerite was also proposed. This high-pressure phase consists of Fe and Ca atoms in sevenfold and ninefold coordination, respectively, while carbonate groups remain in a trigonal planar configuration. This phase could be a candidate structure for dense carbonates in other compositional systems.

Lattice Dynamics and thermodynamic Responses of XNbSn Half-Heusler Semiconductors: A First-Principles Approach

In this work, we have evaluated how CoNbSn, IrNbSn, and RhNbSn half Heusler alloys respond to temperature change and the accompanying lattice vibrations as a cubic crystal. There are reports in the literature for CoNbSn with which we compared our result; there are, however, no reports for the other two alloys except for their Debye temperature obtained via machine learning, and our results compare well. Considering that results in the literature for IrNbSn and RhNbSn are scanty, we first computed the alloys' structural and electronic properties to establish their structural stability using the density functional theory and generalised gradient approximation as implemented in the quantum espresso computational suite. We confirmed the equilibrium lattice structure by exploring the three possibilities for a half Heusler alloy and fitting the results to the state's Murnaghan equation. The negative formation energies obtained supports experimental simulation of the alloys. Results from the lattice dynamics and thermodynamic evaluation show that the alloys favour ionic bonding and are ductile. The Debye temperature positions IrNbSn to be the most promising material for thermoelectric application because it has the least Debye temperature; hence it is supposed to have the lowest thermal conductivity. The Dulong-Petit law is obeyed at high temperature as expected. The phonon dispersion and density of states show that the d orbitals of Co and Nb are the significant contributors to the dispersions at both the acoustic and optical modes of the alloys.

New isostructural halide double perovskites Cs2GeNiX6 (X= Cl, Br) for semiconductor spintronics and thermoelectric advancements

The depletion of fossil fuels and tremendous increase in environmental pollution in the current era has turned the attention of the world's scientists to explore renewable alternative energy resources. Within the first principle calculations, from the Density Functional Theory (DFT) a compact overview on various physical properties of halide perovskites Cs2GeNiX6 (X ​= ​Cl, Br) has been summed up. The obtained values of relaxed lattice constants from the well-known Birch-Murnaghan equation and bond lengths are identical with previously reported values. The calibration of sophisticated Hubbard potential (GGA ​+ ​U) claims Cs2GeNiX6 (X ​= ​Cl, Br) have semiconducting nature with a total magnetic moment of 2 ​μB. Elastically and mechanically alloys are characterized to be stable via checked from their respective cubic elastic packages which display brittle/ductile strength. The flexibility of these perovskite structures suppresses the lattice thermal conductivity, which promotes an exclusive thermoelectric response. The occurrence of such properties in these layered structures lends their broad range of applications in semiconductor spintronics and power technology sources.

Phase transformations of zircon-type DyVO4 at high pressures up to 36.4 GPa: X-ray diffraction measurements

The compression behavior of zircon-type DyVO4 has been investigated in a diamond anvil cell by angle-dispersive X-ray diffraction (ADXRD) at high pressures up to 36.4 GPa. Under quasi-hydrostatic compression with argon as the pressure transmitting medium, DyVO4 underwent a sluggish zircon-to-scheelite phase transformation that started at approximately 8.0 GPa and was completed at 15.3 ± 0.9 GPa. The scheelite-type phase remained stable at pressures up to 25.3 GPa and during the process of decompression to ambient conditions, implying that the zircon-to-scheelite transformation is irreversible. Fitting the pressure-volume data using the third-order Birch-Murnaghan equation of state yielded a bulk modulus B0 = 129 (7) GPa and a pressure derivative of bulk modulus B′ = 3.4 (4) for the zircon-type phase, and B0 = 184 (10) GPa and B′ = 5.3 (8) for the scheelite-type phase. When compressed in a methanol-ethanol (4:1) pressure transmitting medium, DyVO4 was transformed into the scheelite-type phase at a pressure of 8.8 ± 1.1 GPa and then transformed into a fergusonite-type phase at 21.3 ± 1.6 GPa. The scheelite-to-fergusonite transformation was reversible during decompression. Our study indicates that DyVO4 under compression experiences a sequential zircon-scheelite-fergusonite phase transformation and that the scheelite-fergusonite transformation is sensitive to nonhydrostatic conditions.

Can quasicrystals survive in planetary collisions?

We investigated the compressional behavior of i-AlCuFe quasicrystal using diamond anvil cell under quasi-hydrostatic conditions by in situ angle-dispersive X-ray powder diffraction measurements (in both compression and decompression) up to 76 GPa at ambient temperature using neon as pressure medium. These data were compared with those collected up to 104 GPa using KCl as pressure medium available in literature. In general, both sets of data indicate that individual d-spacing shows a continuous decrease with pressure with no drastic changes associated to structural phase transformations or amorphization. The d/d0, where d0 is the d-spacing at ambient pressure, showed a general isotropic compression behavior. The zero-pressure bulk modulus and its pressure derivative were calculated fitting the volume data to both the Murnaghan- and Birch-Murnaghan equation of state models. Results from this study extend our knowledge on the stability of icosahedrite at very high pressure and reinforce the evidence that natural quasicrystals formed during a shock event in asteroidal collisions and survived for eons in the history of the Solar System.