LOW-TEMPERATURE AC CONDUCTIVITY OF OXIDE GLASSES

The electrical conductivity (sigma) of various alkali silicate, berate and germanate glasses has been measured from. 3 K to 300 K in the frequency range 10-100 kHz. Mostly the frequency (omega) and temperature (T) dependence of conductivity below 150 K can be described as sigma similar to T(alpha)omega(beta) where 0 < alpha < 0.25 and 1.0 < beta < 1.15. An abnormal decrease of conductivity with increasing temperature is observed at about 100-150 K in glasses with low alkali oxide concentration(<1 mol%). A theoretical model based on thermally activated excitations of asymmetric double well potential (ADWP) configurations has been used to explain the low temperature conductivity data. From the alkali concentration and size dependence of the parameters in ADWP model, a physical description of the species responsible for low temperature a.c. conductivity is obtained.