Acoustic study of ionic migration and local motion in superionic glasses

An analysis of the acoustic behaviour as a function of temperature in AgI-based superionic glasses is presented. The migration of silver ions appears to have a strong influence on the mechanical spectra in the high-temperature region (T > 77K), giving rise to relaxational losses and dispersions over the whole frequency range (from sub-audio to hypersonic frequencies). A quantitative study of these effects supplies useful information on the microscopic characteristic of the ionic motion. In the low-temperature region (T < 77 K) acoustic anomalies are revealed that are due to thermally activated relaxations (T>10 K) and tunnelling effects (T < 10 K), both arising from some kind of local motion in the glassy network. These peculiarities are discussed in order to understand their origin and their possible connection with the glass-transition temperature Tg.