XCVI. Theory of barium titanate

TLDR

The paper reviews the dielectric and crystallographic theory of barium titanate. The authors compute temperature‑dependent dielectric constants, crystal strains, internal energy, and spontaneous polarization, and use these to estimate undetermined free‑energy coefficients. Expanding the free energy in polarization and strain with reasonable coefficient assumptions explains the crystal transitions, and the study derives relations linking free‑energy coefficients to ionic force constants.

Abstract

Summary The theory of the dielectric and crystallographic properties of barium titanate is considered. By expanding the free energy as a function of polarization and strain and making reasonable assumptions about the coefficients, it is found possible to account for the various crystal transitions. Calculations are made of the dielectric constants, crystal stains, internal energy, and self polarization as functions of temperature. Finally relations are obtained between the coefficients in the free energy and the ionic force constants. These are used to estimate some of the coefficients which are not completely determined by experimental data.