Dielectric Behavior of Barium Titanate in the Paraelectric State

Abstract

The coefficients in the equation of state of BaTi${\mathrm{O}}_{3}$ proposed by Devonshire can be considered as describing the polarization and temperature dependence of the dielectric constant. This dependence has been studied by a dynamic method. The polarization is developed by a large-amplitude at field and the dielectric constant is measured by means of a small rf signal.This method provides an accurate measurement of the coefficient of the ${P}^{4}$ term in Devonshire's equation for the free energy of BaTi${\mathrm{O}}_{3}$. This coefficient has been studied as a function of temperature, and, contrary to previous assumptions, has been found to have a strong temperature dependence, decreasing linearly, with temperature. The fields which can be applied without breaking the samples are not high enough to detect any contribution due to the ${P}^{6}$ term at temperatures as low as only 4\ifmmode^\circ\else\textdegree\fi{}C above the transition to the cubic state.