Syntheses of the perovskite La2CuTiO6 by the ceramic, oxide precursors and sol-gel methods, and study of the structure and Cu-Ti distribution by X-ray and neutron diffraction

The mixed perovskite La2CuTiO6 has been prepared using several methods (classical ceramic, oxide precursors and sol-gel) in order to study the distribution of Cu and Ti in the lattice. This perovskite has an orthorhombically distorted structure [Pnma, standard group no. 62, a = 5.6262(6) Å, b = 7.8396(8) Å, c = 5.5702(6) Å, V = 245.7 Å3] of the GdFeO3 type, and not cubic symmetry as was reported earlier. The different synthetic methods used led to the same phase with different degrees of distortion. Starting from precursor oxides the reaction is faster and by the sol-gel method takes place at lower temperatures than for the ceramic synthesis. Detailed X-ray and neutron powder diffraction studies unambiguously show that Cu and Ti are disordered among the B sites of the perovskite, and give a quantitative idea of the distortion, which is less pronounced than in the case of GdFeO3 itself.We thank the Spanish CICYT (MAT90-1020-C02-01) and the MIDAS Program (92-1592) for financial support, and the Departament d’Ensenyament de la Generalitat de Catalunya for a predoctoral fellowship awarded to M.R.P.Peer Reviewe