RESIDUAL ELECTRON-DENSITY STUDY OF CHROMIUM SESQUIOXIDE BY CRYSTAL-STRUCTURE AND SCATTERING FACTOR REFINEMENT

The crystal structure of chromium sesquioxide, Cr2O3, has been refined from single crystal X-ray diffraction intensity data. Refinement of the scattering factors of Cr and oxygen in the anisotropic stage enabled extension of refinement up to anharmonic terms of the fourth rank tensors (R=0.012). Difference Fourier synthesis shows d-electrons of approximately 0.4eangstrom 3 height situated in six of the eight cube-corner positions around Cr at approximately 0.7angstrom distances; absent at the two positions along the three-fold axis. A prominent peak of 0.9eangstrom 3 height, interpreted as being due to electrons contributing to antiferromagnetic exchange, is situated between Cr pairs of face-sharing CrO6 octahedra. No residual is detected between edge-sharing pairs.