Phenomenological theory of the temperature variation of electrostriction of ferroelectrics in the paraelectric phase

A properly constructed static Landau-Devonshire free energy function implies the validity of the Curie-Weiss law for a homogeneously strained crystal up to first order in the strain and has been used to deduce phenomenological expressions for the temperature dependence of the first order electrostriction coefficients of ferroelectric crystals in the paraelectric phase. If the prototype phase has cubic symmetry, the coefficients Qrs, ij depend linearly on temperature. Moreover, if the ferroelectric transition is of second order the electrostriction coefficients pertaining to shear deformations vanish at the Curie temperature Tc. These theoretical results are in agreement with the experimental data available for perovskite oxides.