Effects of thermal history on the acoustic attenuation of dry and wet B2O3 glasses

The acoustic properties at 10 and 30 MHz of dry and wet boron oxide samples have been investigated over the temperature range between 10 and 300 K. Significant differences in the temperature dependence of acoustic attenuation and longitudinal sound velocity as a function of the annealing treatment and water content have been revealed in the investigated glasses. Measurements, densely performed over the whole temperature range, together with a detailed analysis of the dispersive behaviors, allowed us to evidence the complexity of the relaxational dynamics, as due to the coexistence of different local motions. Above 150 K, the data analysis has been based on the existence of two relaxation processes, whose strengths result to be strictly dependent on the water content. Finally, a possible relation to the empty volume originated from the arrangement of the structural units on nanometer length scale has been put forward.