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 t he distribution of Cu and Ti in the lattice. This perovskite has an or thorhombically distorted structure [Pnma, standard group no. 62, a = 5 .6262(6) angstrom, b = 7.8396(8) angstrom, c = 5.5702(6) angstrom, V = 245.7 angstrom3] of the GdFeO3 type, and not cubic symmetry as was re ported earlier. The different synthetic methods used led to the same p hase with different degrees of distortion. Starting from precursor oxi des the reaction is laster and by the sol-gel method takes place at lo wer temperatures than for the ceramic synthesis. Detailed X-ray and ne utron powder diffraction studies unambiguously show that Cu and Ti are disordered among the B sites of the perovskite, and give a quantitati ve idea of the distortion, which is less pronounced than in the case o f GdFeO3 itself.