The static dielectric constants and their pressure derivatives of KCl, NaCl, LiF, and MgO have been measured at several temperatures ranging from 15 to 295 °K. The samples were prepared in the form of three-terminal parallel-plate capacitors and the dielectric constants were determined from measurements of the capacitance with a high-precision bridge. In all cases the dielectric constants decrease with temperature as does the magnitude of the pressure dependence. Effects of permanent-dipole impurities in NaCl were seen at temperatures around 20 °K. The data were used to calculate the fixed-volume temperature derivative of the dielectric constants. This quantity ${\left(\frac{\partial \epsilon }{\partial T}\right)}_V$, apparently exhibiting the effects of lattice anharmonicity, has a similar temperature dependence for all four compounds: It increases from its room-temperature value as the temperature is lowered, reaches a maximum value at $\frac{T}{{\Theta }_D}\approx 0.15$ (${\Theta }_D=\mathrm{Debye}\mathrm{temperature}$), and then decreases rapidly toward zero at lower temperatures.

• Received 22 June 1972

DOI:https://doi.org/10.1103/PhysRevB.7.3885