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

A careful analysis of ac electrical measurements of the Na2O . 3SiO(2) glass in the temperature range from 2 to 435 K and frequency range 10 to 10(5) 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 omega-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 omega-T region, the UDR and NCL processes are shown to superimpose.