Analysis of AC permittivity response measured in an ionic glass: a comparison between iso and non-iso thermal conditions

AC permittivity is measured on a sodium aluminosilicate glass as a function of frequency and temperature using various experimental conditions. The spectra obtained under isothermal and non-isothermal experiments, with insulating barriers placed on both sides of the sample, are compared. An RC equivalent circuit is proposed to account for the experimental behavior and data are analyzed in terms of activation energy distribution. Then, it is pointed out that the dielectric loss signal measured under ramping temperature and fixed frequency conditions lacks of information in the low temperature range. Therefore, the distribution function obtained in that way must be refined in order to account for the high frequency part of the ac permittivity responses measured at fixed temperature and variable frequency. An additional exponential decay contribution to the distribution function appears thus necessary, though its statistical weight is extremely low. This contribution is akin to the so-called CPA (constant phase angle) or NCL (nearly constant loss) behavior.