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The crystal structures of two molecular phases (I and III) and a polymeric phase (V) of CO2 have been investigated to 60 GPa. CO2-1 (Pa3) transforms to CO2-III (Cmca) at 12 GPa with almost no change of density. Although CO2-III persists in Cmca to at least 60 GPa at ambient temperature, it transforms when heated to 1800 K above 40 GPa to tridymite (P212121) CO2-V with 15.3% volume change. Each car
Crystalline Cs2KMnF6, when prepared below 500°C, adopts a tetragonal elpasolite structure type. Differential scanning calorimetric investigations indicated that Cs2KMnF6 undergoes a phase transition from the low-temperature tetragonal phase (LT) to a high-temperature phase (HT) at about 530°C. Single crystals of the new HT phase could be obtained by annealing a crystalline LT specimen at 600°C fol
Single crystals of Cs2CuCl4 and Cs2CoCl4 have been investigated at high pressures by X-ray diffraction techniques, using a diamond anvil cell. Increasing the pressure to just below 40 kbar caused the crystallinity of Cs2CuCl4 to deteriorate rapidly. This was accompanied by a color change from yellow/orange at lower pressures to deep red, suggesting, e.g., a major change of the coordination geometr
A structural phase transition and the equation of state of the simple-hexagonal (sh) phase, P-V, of phosphorus were investigated at pressures up to 280 GPa using monochromatic synchrotron x-ray diffraction. The P-V phase, which was stable above 137 GPa, has shown a structural transition to a higher-pressure phase, P-VI, above 262 GPa, while the c/a ratio of the sh phase slightly increased with inc
The Pm3̄m to R3̄c high-pressure transition of NbO2F has been studied in detail using diamond anvil cells and synchrotron X-ray radiation. The transition starts at 0.28 GPa and is complete at 0.65 GPa. The bulk modulus for the cubic phase became 24.8 (11) GPa, which is roughly two times higher than for the rhombohedral phase.
The pressure dependence of the crystal structure of cubic tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 (TC) (P <16.0 GPa, T = 298 K) is reported using high-resolution angle-dispersive X-ray powder diffraction. The compound has crystal structures with the molecules in a cubic-close-packed (c.c.p.) arrangement. It shows three phase transitions in the measured pressure range. At ambient conditions, T
High-pressure synchrotron x-ray powder-diffraction studies show that trigonal α-ZrMo2O8 transforms to a monoclinic symmetry phase (δ-ZrMo2O8) at 1.06-1.11 GPa. The space group was determined to C2/m. A further high-pressure transition from the monoclinic δ to a triclinic ε phase occur at 2.0-2.5 GPa (space group P1 or P1). Both transformations are reversible. The volume compressibilities are simil
In situ high-pressure synchrotron X-ray powder diffraction studies of trigonal α-ZrMo2O8, zirconium molybdate, have been performed from ambient conditions to 1.9 GPa, over the α-δ phase transition at 1.06-1.11 GPa. The monoclinic structure of δ-ZrMo2O8, stable between 1.1 and 2.5 GPa at 298 K, has been solved by direct methods and refined using the Rietveld method. Significant distortions of the Z
We report high-pressure Raman, infrared (IR), and optical-absorption spectra of α-ZrMo2O8 (trigonal) up to 38 GPa at room temperature. The spectroscopic studies are consistent with diffraction results that show that α-ZrMo2O8 transforms into δ-ZrMo2O8 (monoclinic) at about 1 GPa and the δ phase converts to the ε phase (triclinic) at about 2.0 GPa. Optical-absorption measurements give an estimate o
High-pressure synchrotron X-ray powder diffraction studies of TiP2O7, ZrP2O7 and ZrV2O7 have been performed. The ZrV2O7 structure undergoes a reversible transition at 1.38-1.58 GPa from cubic α- to pseudo-tetragonal β-ZrV2O7 that displays an orthorhombic 2 × 3 × 3 supercell. At pressures above 4 GPa, ZrV2O7 becomes irreversibly X-ray amorphous. No such transformations are observed for TiP2O7 and Z
The martensitic face centered cubic (fcc)-to-hexagonal close packing (hcp) transformations in xenon were studied using angle-resolved x-ray diffraction patterns. The crystal structure data of xenon over a wide range of high pressure and temperature was analyzed to study the stacking disorders and growth of domains of hcp xenon coexisting with fcc xenon. The analysis confirmed that the formation of
Seismological studies have revealed that a complex texture or heterogeneity exists in the Earth's inner core and at the boundary between core and mantle. These studies highlight the importance of understanding the properties of iron when modelling the composition and dynamics of the core and the interaction of the core with the lowermost mantle. One of the main problems in inferring the compositio
A study was conducted to quantify the extraordinary feature of materials of becoming easier to squeeze when pressure is applied to them. This feature was verified by measurements of P-V relations for cubic iron-nickel alloys for three different compositions: Fe0.64Ni0.36, Fe0.55Ni0.45, and Fe0.20Ni0.80.
The stability of KAISi3O8 hollandite-type structure is investigated in a series of synthesis experiments between 20 and 95 GPa at 650(±50) °C and between 1200 to 2300 °C, using electrically- and laser-heated diamond anvil cells, respectively. Potassium feldspar transformed to a hollandite-type structure in the experimental pressure range from 20 to 95 GPa at temperatures between 1200 to 2300 °C, w
The crystal structures of Nb3Te4 and InxNb3Te4 [x = 0.539 (4)] are reported for a series of pressures between 0 and 40 GPa. Both compounds crystallize in space group P63/m with a = b = 10.671 and c = 3.6468 Å for Nb3Te4, and a = b = 10.677 and c = 3.6566 Å for InxNb3Te4 at ambient conditions. Phase transitions were not observed. High-pressure X-ray powder diffraction was measured using a diamond a
Even under a pressure of 46 GPa, the low-symmetry lone-pair structures of isoelectronic TIF and PbO (see picture for β-PbO), classic examples of systems with a stereochemically active lone pair, resist transformation into the corresponding high-symmetry NaCl and CsCl structures. Ab initio calculations allowed a simple bonding picture for lone-pair structures involving inert-pair elements to be dev
