Low Temperature Heat Capacity and Thermal Expansion of KCI Containing a Low Concentration of Li+

Abstract

The linear thermal expansion coefficient a from 180 mK to 36 K and the heat capacity per gram cp from 0·5 to 10 Kare reported for KCl containing approximately 100 ppm Li+. Contributions to a and cp attributable to the impurity have been identified and analysed on the basis of a model in which the Li + ions reside about 0·05 nm from the equilibrium cationic site in any of the (111) directions. There is consistent quantitative agreement with a Schottky-like term that arises from the eightfold degeneracy of the level splitting; the splitting parameter is 1· 5 K. The large (- 160) Grtineisen parameter associated with the impurity contribution is evidence for a quantum-mechanical tunnelling process, and agrees with values derived from independent measurements of the spectroscopic and dielectric responses of this system under pressure.