Identification of distinctive regimes of behaviour in the ac electrical response of glasses

A careful analysis of ac electrical measurements of the Na2O·3SiO2 glass in the temperature range from 2 to 435 K and frequency range 10 to 105 Hz enables the clear separation of different regimes of behaviour. At the centre of this study is the power-law behaviour called `universal dynamic response' (UDR). It is part of a conductive process which includes the dc conductivity. The domain of dominance of this type of behaviour in ω–T (frequency–temperature) space is determined, and the values of key parameters are obtained for the glass under study. However, the UDR behaviour is only an asymptotic manifestation of a more general relation that becomes important at high temperatures/low frequencies. A totally different process which dominates at low temperatures/high frequencies is that which gives rise to a power law near unity for the conductivity, and therefore, to nearly constant loss (NCL). This behaviour is due to a dielectric relaxation mechanism involving only local ionic motions. In an intermediate ω–T region, the UDR and NCL processes are shown to superimpose.