Theory of Spontaneous Deformation of Barium Titanate

概要

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The spontaneous ferroelectric deformation of the BaTiO_3, crystal to tetragonal form is calculated, taking account of the electrostatic energy and the short-range interaction of the type λγ^9-μγ^<-6>, but neglecting the effect of thernlal motion. It can be deduced that ionic shift causes the lattice spacing to extend a few percent to the same direction (i.e. the direction of spontaneous polarization). The result is sensitive to the choice of the "effective charge" of the Tin ion. However, for a certain range of this parameter, the dependence of the lattice constant on it shows a striking resemblance to the observed dependence of the lattice constant on temperature. Contraction perpendicular to the direction of polarization is a also calculated here considering the interaction among ions. we can show that the extension and contraction suddenly occur when the dipole interaction becomes stronger than some critica value. By taking a proper value for the dipole interaction energy the result can be made to agree with the experimental data.
社団法人日本物理学会の論文
1955-11-05