Phase evolution of lead titanate from its amorphous precursor synthesized by the OPM wet-chemical route

Lead titanate was synthesized by the OPM wet-chemical route by the dissolution of Ti metal in H2O2 followed by the addition of Pb2+ at high pH, resulting in a reactive and amorphous precipitate with (Pb:Ti = 1: 1) mole ratio, which was heat treated between 400degreesC and 700degreesC. The amorphous precipitate was characterized by DSC, and all of the powders were characterized by X-ray diffraction, Raman and XAS (EXAFS and XANES) spectroscopy at the Ti K edge. A metastable, stoichiometric and cubic pyrochlore phase (Pb2Ti2O6, Fd3m) was identified by XRD and Raman spectroscopy up to approx. 450degreesC. Only tetragonal PbTiO3 was identified at higher temperatures. XAS spectra showed that the local structure around the absorbing Ti atom of the intermediate pyrochlore phase is similar to that observed in the amorphous precursor. This fact indicates that the metastable intermediate pyrochlore (Pb2Ti2O6) is kinetically favored to be formed because of its similarity to the amorphous precipitate, instead of the slightly different and thermodynamically favored tetragonal (PbTiO3, P4/mnum) perovskite structure that is only formed at higher temperatures, after the crystallization of the metastable intermediate pyrochlore. (C) 2004 Elsevier Inc. All rights reserved.