XCVI. Theory of barium titanate

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.