Synchrotron X-ray diffraction study on the square-lattice antiferromagnets (CuCl)LaNb2O7 and (FeCl)LaNb2O7

High resolution synchrotron X-ray diffraction methods have been used to study the crystal structure of the two-dimensional square-lattice antiferromagnets (CuCl)LaNb2O7 and (FeCl)LaNb2O7, While the structure of the former is of tetragonal symmetry with simple perovskite unit cell dimensions in the a,b plane (a x a), the latter exhibits a tiny orthorhombic distortion with a 2a x 2a x c superstructure, providing a first example of modulation in the family of transition-metal oxyhalides prepared from topotactic ion-exchange reactions. Possible arrangement in the FeCl layer is proposed. (c) 2006 Elsevier B.V. All rights reserved.