Ultrasonic Relaxations in a Vitreous Ca(NO3)2–KNO3 Mixture

Abstract

Ultrasonic relaxations have been studied in a vitreous 60% KNO3–40% Ca(NO3)2 mixture (mol%) from 1 to 185 MHz in the temperature range 90–130°C. The spectrum of longitudinal relaxation times has been found to be symmetric, fitting a Gaussian distribution in the logarithm of relaxation times, and having a temperature dependent width which narrows remarkably at the high‐temperature end. The occurrence of a high‐temperature sharp distribution of relaxation times in a molten salt system raises a major objection to the currently held belief that the origin of such sharp, high‐temperature distributions, found in molten oxides for example, originate from the covalent nature of the molecular bonds. It has been shown in this paper that a topological model previously proposed by Simmons and Macedo, correlating the distribution of relaxation times to the distribution of molecular environments, provides an excellent qualitative description of the characteristics of the observed relaxation spectra.