Hydrothermal synthesis and structure of lead titanate pyrochlore compounds

Systemic syntheses showed that the lead titanate pyrochlore phases formed under hydrothermal reactions in a certain range of KOH concentrations. The obtained pyrochlore phases all crystallize in the cubic structure. In comparison with typical pyrochlore structure, the O' site in Pb2Ti2O6O' is vacant. In addition, considerable Pb vacancies are present in the samples obtained with high KOH content. Pb(IV) is present in these samples as confirmed by structural and spectroscopic studies. The distribution of metal atoms (Pb and Ti) in pyrochlore phases depends crucially on the KOH content in the starting materials. Higher KOH content tends to form ordered structures where Ti and Pb occupy 16c and 16d positions, respectively. While in the lower KOH content samples, Ti and Pb tend to be randomly distributed within these two sites. The morphology of the pyrochlore samples obtained by hydrothermal synthesis is uniformed spherical aggregates, which are formed by sparsely jointed nanoparticles. Thus, these materials contain narrowly distributed cavities and exhibit rather high surface area. The lead titanate pyrochlore is not stable at high temperature and transforms to the perovskite phase above 651degreesC.