It was noted that, although the frequency-dependent conductivity of ion-containing glasses often exhibited a scale-invariant power-law dispersion at high temperatures, the exponent increased up to unity at lower temperatures. Measurements were made of the conductivity of a series of alkali metaphosphate glasses, including a mixed alkali composition. This demonstrated that the temperature dependence resulted from the superposition of 2 power-law dispersions that originated from a separate mechanism, and did not reflect any intrinsic change in scaling of the process which predominated at high temperatures.

D.L.Sidebottom, P.F.Green, R.K.Brow: Physical Review Letters, 1995, 74[25], 5068-71