Dielectric Behavior of Barium Titanate in the Paraelectric State

The coefficients in the equation of state of BaTiO₃ 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 P⁴ term in Devonshire's equation for the free energy of BaTiO₃. 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 P⁶ term at temperatures as low as only 4^∘{}C above the transition to the cubic state.