High Pressure Structural and Lattice Dynamical Investigations at Reduced Temperatures

Two diamond-anvil pressure cells designed for polycrystalline and single crystal x-ray studies at pressures up to 10 GPa and simultaneously at temperatures down to 2 K are discussed. Recent data concerning the low temperature phase diagram of Bi up to 8 GPa are reviewed along with the salient features of our x-ray detection systems — including energy dispersive facilities. The objectives of our research program on high Tc superconductors are reviewed and some very recent data on V3Si revealing an anomalous increase in the x-ray Bragg scattering on cooling are presented. A preliminary analysis of this anomaly suggests that the low temperature increase in the thermal vibrations may be attributed to the Si atoms and possibly represent a precursor to the martensitic transition.