Phase transitions in ferroelectric solid solutions of complex perovskites

Abstract

The phenomenological theory of ferro- and antiferroelectric solid solutions is proposed taking into account the possibility of compositional order variation. Complex perovskites AB′_0.5B″_0.5O₃ where one of the cations is substituted are considered. The parameter of compositional long-range order in solid solutions is calculated in Bragg-Williams approximation. Formulae for the Curie temperature and permittivity composition dependences are deduced. The theory is in good agreement with the experimental data.