Anomalous frequency dependence of electrical conductivity of low alkali concentration germanate glasses

The existence of the usual Universal Frequency Response (UFR) of ac conductivity, sigma(ac)similar to omega(s) where omega is the angular frequency and s similar or equal to 0.6 is observed for xK(2)O.(1-x)GeO2 glasses with x greater than or equal to 0.02. However, a departure from this power law is observed for a potassium germanate glass containing 0.23 mol% alkali oxide. It appears that this anomaly is a Debye-type dipolar relaxation at very low alkali concentration which transforms into UFR in the high alkali concentration glasses. A similar behavior of conductivity was reported earlier for crystalline quartz containing very low concentration of charge carrier ions.