Reaction Mechanisms in the Formation of Lead Zirconate Titanate Solid Solutions under Hydrothermal Conditions

Reaction mechanisms in the formation of PZT solid solution were studied under hydrothermal conditions (Pb/(Zr+Ti) = 1.0 to 1.9, Zr/Ti = 0/10 to 10/0, 1 M to 5 M KOH, 100° to 220°C, 2 h). A yellow tabular crystallite with tetragonal symmetry and Pb/Ti ～ 2 was formed at 100° to 130°C. A PZT crystallite was formed just above 150°C. The crystallite was a mixture of Ti-rich PZT and Zr-rich PZT phases. When the temperature and KOH concentration were increased, the composition of the PZT product tended to be homogeneous. The PZT in the morphotropic phase boundary zone was formed at Zr/Ti = 5/5, 5M KOH, 220°C, 2 h. Neither PbTiO₃ nor PbZrO₃ was detected as a separate phase under the above hydrothermal conditions.