Relaxational and anharmonic contributions to sound-velocity behavior in superionic glasses

Abstract

An experimental study of the sound velocity in AgI-${\mathrm{Ag}}_2$O-${\mathrm{B}}_2$ ${\mathrm{O}}_3$ superionic glassy systems is presented. Measurements were performed at 5 MHz and in the (77–450)-K temperature range as a function of AgI concentration. The ultrasonic velocity behavior is explained in terms of two physical contributions: The first is due to thermally activated relaxation processes; the second one, to anharmonic effects. Moreover, the analysis of the room-temperature elastic moduli, at increasing concentrations of AgI, seems to give further evidence for the structural hypothesis of a glassy network formed from a matrix of silver borate, in which weakly bonded microdomains of silver iodide are dispersed.