The electron-density distribution and chemical bonding of A15-type Cr obtained by the maximum-entropy method

Abstract

The electron-density distribution of A15-type Cr was obtained by a combination of powder-X-ray-diffraction data and the maximum-entropy method (MEM). Fine powder, in which about 13 vol% BCC Cr was contained, prepared by evaporation of Cr in a low-pressure atmosphere of Ar, was used. Though the powder is composed of the two phases, the final R and RW factors were 0.21% and 0.29%, respectively, and therefore excellent MEM maps were obtained. The MEM maps indicate that the main interaction is a strong covalent bond between adjacent 6c-site Cr atoms within the infinite linear chains. The MEM maps are compared with the valence-electron-density maps of superconducting V3Si and non-superconducting Cr3Si having an A15-type structure. The structure factors for some forbidden reflections, which originate from asymmetric bonding-charge distribution, were also calculated from the MEM densities.