Study of phase transitions and properties of tetragonal (Pb,La)(Zr,Ti)O₃ ceramics-II: Diffuse phase transitions and thermodynamics

The diffuse phase transition in tetragonal PLZT materials has been investigated. Strongly broadened permitivity curves were observed for materials with a relative high La content. Curie-Weiss behaviour in the permittivity curves is observed only at temperatures far above the apparent Curie temperature.A latent heat effect is observed at the sharp FE_t → PE_c transition in PLZT x/30/70 materials with a low La content (x<16 at° La). This heat effect decreases linearly with increasing La content. The diffuse tetragonal → cubic transition is attended with a very small heat-effect and a low value (≈0.04 cal/mol°C) for the entropy difference between high and low temperature phase could be determined.Consequently, polarisation fluctuations are possible in a certain temperature interval around the transition.