Properties of the first and second order memory functions of dielectric relaxation

Abstract The first and second order memory functions (FOMF, SOMF) are obtained considering their definitions given in terms of the complex dielectric permittivity, using numerical methods explained elsewhere and starting from the experimental data. The frequency behaviour of the correlation functions of the dipole-moment and the SOMF are analysed for two glass-forming materials. For a particular window of values of the Havriliak–Negami parameters, the imaginary part of the second order memory function shows an absorption type-band related to dipolar libration effect. Outside of this window this band is not observed. Furthermore, the corresponding first order memory function is presented and we discuss its mid-range variation and its temperature dependence.