Reactions between PbO and TiO2 under Hydrothermal Conditions

The phase relation of products obtained by the reaction between PbO and TiO2 under hydrothermal conditions up to 500 °C and 500 kg/cm2 for 5h has been investigated. The yield and crystallographic properties of purified PbTiO3 depend upon the PbO/TiO2 mole ratio (Pb/Ti ratio) in raw mixtures as well as the reaction temperature. Both PbTiO3 and PbTi3O7 are synthesized at a remarkably low temperature under hydrothermal conditions, as compared with the ignition process in air. Pure and well-crystallized PbTiO3 is obtained by heat-treating above 400 °C at Pb/Ti ratios greater than 1.0 and by dissolving excess PbO with acetic acid. PbTi3O7 coexists occasionally with PbTiO3 to some extent at Pb/Ti ratios less than 1.0, but appears as a single phase in the temperature range 100–450 °C at the Pb/Ti ratio 0.33. The unit cell volume of PbTiO3 prepared at lower temperature is considerably large, suggesting a loosely-packed structure. The compound is always of tetragonal form containing no metastable cubic form.