Dielectric Constant in Perovskite Type Crystals

Slater's theory of the dielectric constant in BaTi${\mathrm{O}}_{3}$ has been extended by treating the ionic polarizability quantum mechanically instead of classically. This leads to an expression for the dielectric constant which is good at all temperatures and shows a deviation from the Curie-Weiss law at low temperatures. The theory is applied to SrTi${\mathrm{O}}_{3}$ and to KTa${\mathrm{O}}_{3}$ above its transition at 13.2\ifmmode^\circ\else\textdegree\fi{}K.