Brillouin scattering in alkali metaphosphate glasses and melts

We report the results of Brillouin scattering measurements performed on a s eries of alkali metaphosphate glasses and melts including the mixed alkali composition. Using independent viscosity data, we have applied a time-tempe rature superposition approach to obtain from the relevant features of the B rillouin spectra the relaxation characteristics of the complex longitudinal elastic modulus. A mixed alkali effect is evidenced in the Brillouin scatt ering which occurs in the gigahertz range. We find a relaxation process tha t can be described by a Kohlrausch function with beta approximate to 0.30 f or single alkali compositions, but is narrower (beta approximate to 0.40) a t the mixed alkali composition. (C) 1999 Elsevier Science B.V. All rights r eserved.