The effect of monovalent impurities on KCl low‐temperature specific heat

Abstract

An enhancement of the specific heat of KCl crystals doped with Ag+ and Na+ impurities in the temperature range 5 to 30 K is observed. A comparison of the experimental results with the theory shows that in the case of Ag+ the force constants (FC) are weakened by four times. Theestablished quasi-local frequency (QLF) is close to that found in experiments of infrared absorption. The anomalous increase of the low-temperature specific heat of the KC1 crystals withlight substitutional Na+ impurities are ascribed to the vibration of isolated ions with FC weakened 2.5 times.