THE STATIC DIELECTRIC CONSTANT OF NaCl, KCl, AND KBr AT TEMPERATURES BETWEEN 4.2 °K AND 300 °K

Abstract

Measurements of the static dielectric constant, εst, were made, using a transformer bridge with an absolute error of about 0.5% and a relative error of less than 0.02%. At 300 °K, the values obtained for εst were 5.90, 4.81, and 4.88, while 104(1/εst)(∂εst/∂T)p, was found to be 3.21, 2.93, and 3.10 (°K)−1 for NaCl, KCl, and KBr respectively, in good agreement with other recent measurements.At low temperatures, the curve of εst versus temperature was found to show a minimum, but it has not been found possible to explain all of the observed increase in εst with decreasing temperature below the minimum by the presence of impurities.The variation of εst with temperature is analyzed in detail on the basis of the evaluation made by Szigeti of the anharmonic contribution, G, to the dielectric constant. Estimates of (∂εst/∂T)v, which is equal to (∂G/∂T)v according to Szigeti (1961), have been made from the experimental data, and the curves of (∂εst/∂T)v versus temperature show an unexpected maximum at a temperature near θD/4,where θD is the Debye temperature.