Residual electron density study of chromium sesquioxide by crystal structure and scattering factor refinement

Abstract

The crystal structure of chromium sesquioxide, Cr 2O 3, 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 ∼ 0.4ρ A ̊ 3 height situated in six of the eight cube-corner positions around Cr at ∼ 0.7 A ̊ distances; absent at the two positions along the three-fold axis. A prominent peak of 0.9ρÅ 3 height, interpreted as being due to electrons contributing to antiferromagnetic exchange, is situated between Cr pairs of face-sharing CrO 6 octahedra. No residual is detected between edge-sharing pairs.