Acoustic properties and diffusion in superionic glasses

Abstract

An ultrasonic study of the loss characteristics and sound velocity was carried out in AgI-${\mathrm{Ag}}_{2}$O-${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$ glasses as a function of temperature and silver-compound concentration. From the behavior of the sound velocity in ${({\mathrm{Ag}}_{2}\mathrm{O})}_{y}{({\mathrm{B}}_{2}{\mathrm{O}}_{3})}_{1\ensuremath{-}y}$, the formation of fourfold-coordinated boron ions is suggested. This increases rapidly, as a function of $y$, until $y\ensuremath{\simeq}0.25$; for larger $y$, a strong production of singly bonded oxygen ions (nonbridging oxygen ions) prevails, which weakens the glassy network. From the analysis of the attenuation peaks in terms of a relaxation-time Gaussian-type distribution, arising from the thermally activated relaxation of mobile silver ions, it is argued that there exists a similarity between the ion motion in a stress field and in an electric one. By way of this analogy and by combining the ultrasonic results with the dc conductivity data in ${(\mathrm{AgI})}_{x}{[{({\mathrm{Ag}}_{2}\mathrm{O})}_{y}{({\mathrm{B}}_{2}{\mathrm{O}}_{3})}_{1\ensuremath{-}y}]}_{1\ensuremath{-}x}$, the ion-jump distances are calculated. The behavior with AgI concentration is consistent with the structural hypothesis of the existence of silver ions differently bonded and mobile in the glassy matrix.