An Investigation of Insulating La4BaCu5O12 Obtained by the Reduction of Metallic La4BaCu5O13.1

The structure of insulating La4BaCu5O12 obtained by the reduction of metallic La4BaCu5O13.1 has been studied by using electron microscopy and high-resolution X-ray diffraction data. While La4BaCu5O13.1 (P4/m) has a tetragonal structure with the supercell ac 5 × ac 5 × ac , the reduced phase, La4BaCu5O12, is monoclinic (P2/m) with the supercell ac 5 × ac × ac 5 . La4BaCu5O12 consists of CuO5 square pyramids and CuO4 square planar units, instead of CuO6 octahedra and CuO5 square pyramids as in La4BaCu5O13.1. Electron microscopic examination reveals the presence of twinning in some of the crystals of La4BaCu5O12.