Cálculo da susceptibilidade do modelo ordem-desordem de oito sítios para ferroelétricos

Abstract

In this work we calculate both static and dynamical dielectric tensors for the perovskite BaTiO3. The calculations in the static case, performed for all the phases presented by the compound are based on the thermodynamical properties of an order-disorder model of ferroelectrics, proposed by Comes, Lambert and Guinier. We assume no crystalline distortion of the unitary cell in the different phases. The structural change is considered afterwards, leading us to the exact solution of stability in each phase, within the correct temperature domains. In the dynamical case, the calculation is done for the C4V symmetry phase, for the direction parallel to the spontaneous polarization, and for the Oh symmetry phase. It is performed from dynamical equations for the populations of the eight sites and the transition probabilities calculated by means of the Eyring equation. The result obtained agree with the static limit and presents a relaxation term of Debye type.