Structural analysis of CuGeO3: Relation between nuclear structure and magnetic interaction

The structure of CuGeO3 has been analyzed by means of x-ray and neutron 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 from 295 to 20 K may be characterized by a rotation of the Cu[O(2)](2) ribbons around the c axis. It is related to the distortion below the spin-Peierls transition, and has an impact on the magnetic interaction parameter J. For the distorted structure in the spin-Peierls phase, based on a large set of superstructure reflections, we qualitatively confirm the proposed model (space group Bbcm) with a slightly different direction of the oxygen displacements. A computation of J reveals that its splitting in the spin-Peierls phase is dominated by the modulation of the Cu-O-Cu bond angle.