Negative electrocaloric effect in antiferroelectric PbZrO₃

The dielectric and thermal properties of a typical antiferroelectric (AFE) material are investigated by minimising numerically the free energy as given by the Kittel model of AFEs. The phase line of second-order phase transitions in the E-T phase diagram is shown to change to a first-order line at the tricritical point T3cp, E3cp. The static dielectric susceptibility and the electrocaloric (EC) effect are calculated as a function of temperature and the applied electric field E. It is found that in a given range of electric fields and temperatures the EC effect has negative values but generally becomes positive above the AFE ordering temperature T0. The dielectric susceptibility shows characteristic peaks at the phase transitions between the field-induced polar and the AFE antipolar phase, and diverges at the tricritical point. We present experimental results for a negative EC effect, which have been obtained by direct EC measurements in PbZrO3 ceramics, and agree qualitatively with the above model.