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 T-3cp, E-3cp. 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 T-0. 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. Copyright (C) EPLA, 2014