The phase stability of YbVO4 under pressure has been investigated using synchrotron based angle dispersive x-ray diffraction and Raman spectroscopic techniques up to 34.5 and 26.5 GPa, respectively. The results indicate that the compound transforms from the ambient pressure zircon structure to the scheelite structure above 5.9 GPa with 11.8% volume discontinuity. The coexistence of the two phases is observed over a large pressure range. At 15.8 GPa, the (011) peak of the scheelite phase develops asymmetry, and the pattern at further high pressures could be fitted to a fergusonite-type monoclinic structure. On reducing the pressure, the fergusonite phase reverses back to the scheelite phase; the latter phase could be recovered as a metastable phase at ambient pressure. The refined structural parameters along with the equation of state are given for various phases of YbVO4. Changes in the vibrational properties across these transitions, particularly across the scheelite↔fergusonite transition, have been investigated using Raman spectroscopy.

High pressure angle dispersive x-ray diffraction measurements are carried out on LuVO 4 in a diamond anvil cell up to 33 GPa at the Elettra synchrotron radiation source. The measurements show that LuVO 4 undergoes a zircon to scheelite structure phase transition with a volume change of about 11% at about 8 GPa. A second transition to a monoclinic fergusonite structure occurs above 16 GPa. The data are also recorded while releasing the pressure, and indicate that the scheelite phase is metastable under ambient conditions. The equations of state and changes in internal structural parameters are reported for various phases of LuVO 4 . Lattice dynamical calculations based on a transferable interatomic potential were also performed and the results support the stability of the scheelite structure at high pressures. The calculated structure, equation of state and bulk modulus for all the phases are in fair agreement with the experimental observations.

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The effect of pressure on structural properties of potassium and rubidium is studied with diamondanvil cells by energy-dispersive x-ray diffraction with synchrotron radiation at room temperature up to 50 GPa. The K III structure of potassium at pressures above 23 GPa is indexed by the use of a tetragonal-body-centered lattice (tI16) with 16 atoms in the unit cell. A new phase is found for rubidium above 46 GPa. Equation of state data for these heavy alkali metals are presented and compared with earlier data for cesium.

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Electrical resistivity, thermoelectric power, and high-pressure x-ray-diffraction measurements are carried out to investigate the anomaly observed earlier in fusion data around 3 GPa in the intermetallic compound AuIn 2 . While the imaging plate high-pressure angle-dispersive data indicate a structural phase transition beyond 8 GPa, the thermoelectric power shows a peak around 2 GPa, indicating the occurrence of an electronically driven isostructural transition. The first-principles linearized muffin-tin orbital calculations reveal that this transition is brought about by interception of the Fermi level by the energy-band maximum. The Lifshitz nature of this transition is responsible for the anomaly in the high-pressure electrical and fusion data.

Crystalline resorcinol [C6H4(OH)2] has been shown to amorphize at 40 kbars, solely using Raman scattering. The external modes vanish resulting in a spectrum similar to the density of states spectrum, but the internal modes persist indicating a breakdown of translational and orientational correlation between the molecules. The amorphous state recrystallizes after the pressure is released. We also provide additional information on the known a to P phase transition.

An easily assembled setup employing diamond anvil cell, stainless steel gasket and leads, and mylar embedded Al2O3 (alumina) pressure medium for the measurement of electrical resistance of materials under pressure is described. The use of a mylar sheet prevents the alumina layer from sticking to the anvil in the precompacting stage of Al2O3 and also reduces the pressure gradients in the final assembly. The technique is used to reproduce the known transition in Si, Ge, and Fe. The results of measurements of electrical resistance of ytterbium up to 40 GPa are reported. In the hcp phase of ytterbium the electrical resistance increases with pressure. Efforts are made to explain the variation of resistance with pressure from known band structure calculations.