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Abstract
According to Smolensky's model,1 the microregions (Kanzig regions), that the ferroelectrics with diffuse phase transition (DPT) are composed of, are polarized uniformly. The entire properties (such as permittivity ⟨ε⟩) of ferroelectrics are the statistical average results of the Kanzig regions. We consider that the polarization in each Kanzig region is not uniform, but is Gaussian distributive. Therefore, the Gibbs function density for ferroelectrics depends not only on polarization P, but also on (ΔP). By Landau's theory, it is shown that the relation of the permittivity ε of a Kanzig region and temperature T is the same as the ordinary, but the relation of the Curie-Weiss temperature of a Kanzig region which polarization P is Gaussian distributive and the Curie-Weiss temperature
0, of the Kanzig region which polarization is uniform is
where α is the coefficient of the (VP)2 in the Gibbs function density, γ is the average length of Kanzig region and C is Curie's constant.