Synthesis, structure determination from powder diffraction data and thermal behaviour of titanium(IV) oxalate [Ti2O3(H2O)(2)](C2O4)center dot H2O

A titanium(IV) oxalate, [Ti2O3(H2O)(2)](C2O4).H2O, has been synthesised in a polycrystalline form in the course of the study of precursors of PZT type oxides. Its crystal structure has been solved ab initio from powder diffraction data collected with conventional monochromatic X-rays. The symmetry is orthorhombic, space group Cmca, with cell dimensions a = 15.494(2) Angstrom, b = 10.491 (1) Angstrom, c = 9.700(l) Angstrom and Z = 8. The structure consists of inorganic corrugated layers of corner-sharing TiO6 octahedra, which form infinite -Ti-O-Ti- connections, linked together by the oxalate anions. The titanium environment is discussed with regard to bond-valence calculations. The thermal behaviour of this compound has been studied by temperature-dependent X-ray diffraction and thermal analyses. In the course of the dehydration process, the partially dehydrated phase [Ti2O3(H2O)(2)](C2O4) has been isolated and its structure has been solved from in situ X-ray powder diffraction data. Its crystal structure determination has shown that the framework of the precursor is preserved. The complete decomposition scheme into anatase is also described. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.