Phase Equilibrium in the System PbO‐TiO ₂ –ZrO ₂

Phase equilibrium relations in the system PbO–TiO 2 –ZrO 2 were studied by quenching in the range where the PbO content is 50 mole % and more. Isotherms were examined at 1100°, 1200°, and 1300°C and tie lines were determined between the liquid and solid solution in equilibrium. The incongruent melting point of PbZrO 3 was 1570°C and the equilibrium between liquid, PbO‐type solid, and PbZrO 3 is peritectic. Pb(Zr,Ti)O 3 solid solutions containing more than 14 mole % PbZrO 3 decomposed to liquid, ZrO 2 , and Pb(Zr,Ti)O 3 and the decomposition temperature rises from 1340° to 1570°C with increasing PbZrO 3 content. The system PbTiO 3 –PbZrO 3 should not be treated as a binary, but as a section of the ternary system.