Study of phase transitions and properties of tetragonal (Pb,La)(Zr,Ti)O₃ ceramics-I: Phase diagram and β-phase

The phase diagram (T-x plot) of thermally depoled tetragonal PLZT materials has been investigated by means of X-ray diffraction, Capacitance and DSC measurements. Materials with a low La content show a classical Fe_t↔PE_c transition. This transition has first or second order character, dependent on the Zr/Ti ratio. Materials with a medium and high La content show a diffuse transition from the cubic high temperature phase to a tetragonal, so called β phase. This β phase has no clear FE properties and a spontaneous transition to the FE_t phase on lowering the temperature only takes place for materials with a medium La content. For materials with a high La content a spontaneous β_t→ FE_t transition is not observed.