Thermal decomposition of lanthanum-titanium citric complexes prepared from ethylene glycol medium

Abstract

The paper addresses the thermal decomposition of La-, Ti- and bimetallic La-Ti-non-crystalline citric complexes, prepared in ethylene glycol medium. The latter complex is the starting material for the effective ferroelectric La₂Ti₂O₇ preparation by the polymerized complex method. Based on thermogravimetric analysis (DTG, DTA and TG) and identification of some of the intermediates (by elemental analysis, NMR and IR spectroscopy and X-ray diffractometry), it is established that the thermal destruction proceeds step-wise, starting with dehydration above 50–60°C, partial transformation of the citrate to aconitate up to 200°C, followed by releasing of the ethylene glycol bonded as adduct and ester (200–280°C) and decarboxilation (280–335°C). The complete destruction of the organic components results in mixed-metal oxocarbonate. The process is completed at ∼750°C giving poorly crystalline La₂Ti₂O₇. The results obtained are compared with those for a water-prepared NH₄-La-Ti-citric complex.