Paraelectric-Ferroelectric Phase Boundaries in Semiconducting Perovskite-Type Crystals

Abstract

The formation of first-order paraelectric-ferroelectric phase boundaries in semiconducting crystals of the ferroelectrics K${\mathrm{Ta}}_{0.65}$${\mathrm{Nb}}_{0.35}$${\mathrm{O}}_{3}$ and BaTi${\mathrm{O}}_{3}$ has been studied. It is shown that in crystals having carrier concentrations greater than ${10}^{16}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, sharp first-order phase boundaries can form during the paraelectric-ferroelectric phase transformation, and that such a transformation results in the formation of reproducible single-domain crystals. The direction of the cubic-to-tetragonal phase boundary is found to differ from a {110} lattice plane by approximately 5\ifmmode^\circ\else\textdegree\fi{}, i.e., the boundary-plane normal is 40\ifmmode^\circ\else\textdegree\fi{} from the direction of the crystal $c$ axis. This result is in excellent agreement with existing crystallographic theories. Data are also presented on the infrared photo-ionization absorption anisotropy and the electrical resistance anisotropy measured on a single-domain semiconducting crystal of K${\mathrm{Ta}}_{0.65}$${\mathrm{Nb}}_{0.35}$${\mathrm{O}}_{3}$.