PRESSURE-INDUCED PHASE-TRANSITION IN CSGEBR3 STUDIED BY X-RAY-DIFFRACTION AND RAMAN-SPECTROSCOPY

We have investigated the effect of hydrostatic pressure on the structu ral properties of CsGeBr3 by means of X-ray diffraction and Raman spec troscopy. Pressures were generated using diamond anvil cells. At 1.0(2 ) GPa the trigonal ambient pressure modification of CsGeBr3 undergoes a reversible first-order phase transition to a high-pressure polymorph crystallizing in the cubic perovskite structure. The variation in Ge- Br bond length is obtained from single-crystal structure refinements o f both the low- and the high-pressure modifications. The phase transfo rmation occurs at a relative volume of V/V-0 = 0.92, and the predictio n from Hartree-Fock calculations is in agreement with this experimenta l result. (C) 1995 Academic Press, Inc.