Born model repulsive interactions in the alkali halides determined from ultrasonic data

Abstract

Abstract Recent studies of the Born Model of the Li, Na, K and Rb halides using ultrasonic data are summarized. It is shown that, when ultrasonic values of the temperature and pressure derivatives of the bulk modulus are used in the Hildebrand approximation for vibrational terms in the free energy, the stiffness π = − r 2 W ″ R / rW ′ R of the net repulsive interaction, W R , exhibits a smooth and regular behavior when plotted against nearest neighbor distance, d o . This contrasts with the erratic behavior of the repulsive stiffnesses when hydrostatic compression data are employed. Numerical values of the ultrasonic W R and π are given. The experimental stiffnesses compare well in their pattern with a recent comprehensive set of theoretical values (exchange charge model) calculated by Hafemeister and Zahrt. A possible improvement of the theory is pointed out.