On the empirical functions describing the α-relaxation of glass-forming systems

In the present work a comparison among the different functions commonly used to describe the α-relaxation in glass-forming systems has been established. The main results obtained are: (i) By using a direct Fourier transformation we have corroborated previous results, which were obtained by different means, connecting the Havriliak–Negami (HN) and Kohlrausch–Williams–Watts (KWW) descriptions. (ii) An equivalence between the latter description and the one obtained from the Rajagopal distribution has been established in a very wide range. Thus, an expression for the distribution function of relaxation times, valid for most of the stretched exponential behaviours experimentally found, has been derived. (iii) Comparing these three functions with the dielectric relaxation data from different systems, we proposed a criteria for the choice of the most appropriate function depending on the particular type of the glass former system.