The gruneisen parameter of the softferroelectric mode in the cubic perovskites†

It is shown that because of the unique properties of the soft ferroelectric mode in perovskites of the BaTiO3-type, as well as in related displacive ferroelectrics, the Gruneisen parameter γf of this mode and its temperature dependence can be simply determined from measurements of the pressure and temperature dependences of the static dielectric constant ε in the cubic paraelectric phase. γf is given by the relationship γf = ε/2xC*, where x is the isothermal volume compressibility and C* is a constant determined from the pressure measurements. The product xC* is very nearly temperature-independent so that the temperature dependence of γf reflects that of ε and thus γf obeys a Curie-Weiss law. The necessary data are given for SrTiO3, KTaO3, BaTiO3 PbTiO3 PbZrO3 and PbHfO3.