STRUCTURAL-ANALYSIS OF CUGEO3 - RELATION BETWEEN NUCLEAR-STRUCTURE AND MAGNETIC INTERACTION

The structure of CuGeO3 has been analyzed by means of x-ray and neutro n single-crystal diffraction as a function of temperature. There is a pronounced temperature dependency of the atomic positions in the high- temperature Pbmm phase. The observed deformation scheme on cooling fro m 295 to 20 K may be characterized by a rotation of the Cu[O(2)](2) ri bbons around the c axis. It is related to the distortion below the spi n-Peierls transition, and has an impact on the magnetic interaction pa rameter J. For the distorted structure in the spin-Peierls phase, base d on a large set of superstructure reflections, we qualitatively confi rm the proposed model (space group Bbcm) with a slightly different dir ection of the oxygen displacements. A computation of J reveals that it s splitting in the spin-Peierls phase is dominated by the modulation o f the Cu-O-Cu bond angle.