Sound velocity behaviour in silver borate glasses

The sound velocity behavior of 5 MHz longitudinal and transverse waves in silver iodide-silver borate glasses show in the 77–430 K temperature range the presence of dispersive effects, whose contribution increases with the AgI content. These effects arise from the thermally activated jumps of Ag+ ions, between nearly equivalent positions available in the glassy network. The whole behavior was explained by the overlap of two different mechanisms : the relaxational one and the one coming out from the anharmonicity of the system. This last effect implies, in a quasi-harmonic approximation, a linear temperature dependence of the elastic constants in all the explored ranges.