Crystal structure and possible charge ordering in one-dimensional Ca3Co2O6

The crystal structure of the one-dimensional oxide Ca3Co2O6 has been solved by ab initio methods from powder X-ray diffraction data and refined from powder neutron diffraction data. The structure is closely related to that for Sr3NiIrO6. Ca3Co2O6 crystallizes in space group R-3c, Z = 6 (hexagonal setting) and a = 907.93(7) and c = 1038.1(1) pm. The Co atoms form alternating, face-sharing coordination polyhedra of trigonal prisms and octahedra. In this way one-dimensional Co-O chains are formed that run along the trigonal axis. The chains are separated by eight coordinated calcium atoms. The separation between Co atoms within the chains are 259.5 pm which suggest metal-metal interactions. Based on interatomic Co-O distances and bond strength considerations, it is proposed that either charge or spin ordering of the different Co species occurs within the chains. (C) 1996 Academic Press, Inc.