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 400°C and 700°C. 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. 450°C. 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/mmm) perovskite structure that is only formed at higher temperatures, after the crystallization of the metastable intermediate pyrochlore.