Neutron diffraction study of the oxychloride layered perovskite, (CuCl)LaNb2O7

The structure of the oxychloride layered perovskite, (CuCl)LaNb2O7, has been examined by neutron diffraction. Rietveld refinement of room temperature neutron TOF data, while consistent with the previous X-ray study, allows for an improved modeling of the structure. The structure consists of double perovskite layers (LaNb2O7) separated by copper chloride layers. The copper is octahedrally coordinated, bridging between apical oxygens from the perovskite layer and surrounded by four chlorines in the Cu-Cl plane; this gives rise to edge-sharing CuO2Cl4 octahedra. The chlorines within the Cu-Cl plane were found to move off the ideal (0, 0, 1/2) position to a more general position, (x, 0, 1/2). This disorder leads to a combination of four short and two long distances, common to the Jahn-Teller distorted environments for d(9) copper. Structural details are discussed with respect to their influence on the chlorine disorder. (C) 2002 Elsevier Science Ltd. All rights reserved.