X-Ray and Neutron Diffraction Study of CaBi2O4

The crystal structure of the 1:1 CaO-Bi2O3 compound (CaBi2O4) has been determined by single crystal X-ray and neutron powder diffraction techniques. The compound crystallizes with the symmetry of the monoclinic space group C2/c and lattice parameters a = 16.6130(5) Å, b = 11.5900(4) Å, c = 13.9939(4) Å, β = 134.048(1)°. The structure consists of sheets parallel to the b-c plane and connected by Ca-O bonds. There is a structural unit in each layer consisting of four Bi atoms, ten oxygen atoms, and two calcium atoms. The Bi atoms are fourfold coordinated and the coordination polyhedron may be described as a short distorted pyramid, open on one end to accommodate the lone-pair electrons of the bismuth atoms. Calcium is seven-coordinated and the coordination polyhedron may be described as a monocapped trigonal prism.