The electron distribution in corundum. A study of the utility of merging single-crystal and powder diffraction data

Abstract

Powder X-ray diffraction data for corundum were collected by a variety of methods and reduced to structure amplitudes by two profile-fitting techniques. The resulting averaged powder-data set was merged with three different single-crystal data sets to assess the improvements possible over least-squares modelling of extinction for accurate electron density analysis of minerals. With reference to the deformation electron density derived from multipole refinements, it is concluded that this strategy offers advantages over the post facto modelling of severe extinction effects commonly observed in such systems. The deformation electron density is found to be in quantitative agreement with the results of recent ab initio calculations on clusters and the bulk.