Electrostrictive effects in antiferroelectric perovskites

Electrostrictive terms have been introduced into the simple Kittel free-energy function for antiferroelectrics. An additional coefficient W is found to be required to take account of the interaction with the sublattice polarizations, and Q and W values have been calculated from experimental data for typical antiferroelectric perovskites PbZrO₃ and Pb(Mg _1/2W_1/2)O₃. Consideration of several ferro- and antiferroelectric perovskites suggests that the magnitude of Q is not affected strongly by ferro- or antiferroelectricity, but that it does depend quite strongly upon any disorder in the cation arrangement. An empirical rule that the product of the electrostrictive Q coefficient and the Curie Weiss constant C is almost the same for all ferro- and antiferroelectric perovskites is proposed (Q_hC = 3.1±0.4×10³ m⁴ C ^-2 K). A very simple "rattling ion" model is shown to give a simple intuitive explanation of the observed results.