X-ray charge density study of chemical bonding in skutterudite CoSb3

The experimental charge density of nondoped CoSb3 has been determined by the maximum entropy method (MEM) using low temperature (10 K), short wavelength (0.42 A), and high-resolution (d(min)=0.33 A) synchrotron x-ray powder diffraction data measured at SPring-8, Japan. The MEM charge density clearly reveals three types of charge density overlap between atoms in CoSb3. The four Sb atoms form an Sb-4 ring, and the MEM charge densities at two types of Sb-Sb midpoints are 0.35 and 0.50 e A(-3). The charge density overlap between the Co and Sb atoms at the midpoint is 0.52 e A(-3), which is larger than the values observed at the Sb-Sb midpoints. The nature of the chemical bonding observed in the present MEM charge density is consistent with a previous theoretical study by Lefebvre-Devos.