The internal friction and the dielectric losses of Na-K metaphosphate glasses have been investigated. A single alkali and a mixed alkali internal friction peak were observed. The single alkali peak shifted to higher temperatures with increasing concentration of the second alkali and eventually disappeared. The activation energy of this peak increased with the alkali mixing ratio. As in silicate and borate glasses, the single alkali peak correlates closely with the dielectric loss. The mixed peak showed a dramatic increase in size with the addition of the second alkali, but the activation energy was practically independent of the alkali mixing ratio. The large reduction in height of the mixed peak, observed on annealing, is discussed together with the influence of water.
van Ass, H. M. J. M., & Stevels, J. M. (1974). Relaxation processes in mixed alkali Na-K methaphosphate glasses. Journal of Non-Crystalline Solids, 14(1), 131-141. https://doi.org/10.1016/0022-3093(74)90024-6