CRYSTAL-STRUCTURE OF CUGEO3 UNDER PRESSURE

We have investigated the crystal structure of orthorhombic CuGeO3 unde r hydrostatic pressure (P<6.5 GPa, T=298 K) using high-resolution angl e-dispersive x-ray powder diffraction. A nonlinear compression behavio r is observed for all three crystallographic axes. Full profile refine ments of the diffraction patterns provide the internal structural para meters in the stability range of the ambient pressure phase. The main structural changes induced by pressure consist of tilting of the CuO4 ribbons around the c axis and a large decrease of the Cul-Ol bond dist ance. Possible implications of these results for the explanation of th e strong pressure dependence of the spin-Peierls transition temperatur e are discussed. [S0163-1829(97)52242-9].