In order to quantify the thermally activated relaxation of mobile Ag ions in super-ionic phosphosulfate and phosphosulfide glasses, previously reported broad attenuation peaks were analyzed in terms of a Gaussian-type energy distribution. The parameters which were obtained were used to determine the effect of thermally activated relaxation processes upon the temperature dependence of the ultrasonic wave velocities that were measured at temperatures of between 1.5 and 300K. After subtracting the relaxation effects, together with those which were due to anharmonic interactions, another contribution to the temperature dependence of the ultrasonic velocity was found to remain at temperatures below 100K. This obeyed the linear temperature dependence which was predicted by the soft-potential model for the relaxation of soft harmonic oscillators. The soft harmonic oscillator relaxation contribution to the ultrasonic velocity temperature dependences of Ag phosphate-based glasses had a similar magnitude to those which had been previously determined for lanthanide metaphosphate glasses. Whereas the Ag phosphate-based glasses had skeletons that comprised long chains of phosphate ions, the lanthanide metaphosphate glasses had an almost 3-dimensional structure. The agreement of the excess contribution to the temperature dependence of the ultrasonic velocity, with the predictions of the soft-potential model for both types of glass (in spite of their complete difference in structure), was suggested to be further evidence for the universal applicability of the soft-potential model. In order to determine the vibrational anharmonicity of the long-wavelength acoustic modes in super-ionic glasses, the hydrostatic pressure derivatives of the second-order elastic stiffness tensor components were measured for the various glasses. The thermal expansions of the vitreous phosphates were also measured. It was found that the linear thermal expansion coefficient became anomalously negative at lower temperatures.

G.A.Saunders, R.D.Metcalfe, M.Cutroni, M.Federico, A.Piccolo: Physical Review B, 1996, 53[9], 5287-300