Abstract
The electron density distribution in magnesium chromium oxide spinel [composition MgCr 2O 4; for general formula TX 2O 4, tetrahedral site T = Mg xCr 1 − x, octahedral site X = Cr 1 + xMg 1 − x, x = 0.984(6)] has been studied with single-crystal X-ray diffraction methods through scattering factor refinement procedures. In the refinement with harmonic parameters, there are electron density residuals around the X-site; six residuals of −1.0e/Å 3 height along, eight of +0.7~0.8e/Å 3 height avoiding the directions toward the coordinated oxygens. Also, a +0.6e/Å 3 height residual is seen near oxygen along the T-O direction. These residuals almost completely disappear with anharmonic refinement. Another residual (in harmonic refinement, +1.27e /Å 3; anharmonic, +0.90e/Å 3 in height) is situated at the center of the X 4O 4 cuboidal unit in the structure. [230 equivalent-averaged reflexions, R = 0.0091 (harmonic refinement), R =0.0064 (anharmonic refinement)]
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