Two distinct physical processes contribute to the temperature dependence of the low-frequency dielectric constant: the effect of thermal expansion on ionic and electronic polarizabilitiesAND DENSITY AND A PURE TEMPERATURE EFFECT WITH THE VOLUME HELD CONSTANT. The contributions from these processes can be determined from separate measurements of the temperature and pressure coefficients of the dielectric constant. The temperature coefficient at constant volume is due to both the anharmonic terms in the expansion of the lattic energy as a function of ionic displacements and the nonlinear dependence of the polarization on ionic displacements. It is possible to explain qualitatively why the temperature coefficient at constant volume changes from positive to negative as the dielectric constant increases. A correlation can be made between various temperature effects and the infrared absorption spectrum. (Author).