Configuration entropy and non-Arrhenius behavior in the α relaxation of glassy dielectrics

Applying Eyring equation to experimental data for the α relaxation of glassy dielectrics shows the fundamental role of the activation entropy in the relaxation dynamics. The combination of Eyring equation and compensation law gives access to other important parameters, such as the compensation temperature and the absolute value of the configurational activation entropy, ΔS_C, in the Arrhenius regime. The non linear behavior observed at low temperatures is explained by the time and temperature variation of the configurational activation entropy. We propose that this change corresponds to the rarefaction of free equilibrium states as T is lowered. A simple method is proposed to calculate ΔS_C from the change of free energy in the non linear regime. The lowest temperature limit of the a relaxation is not known but it seems unlikely that it would be the VTF or the Kauzmann temperatures. Brief comments on the physical significance of these two parameters are made. It is also shown that relaxation times are not invariant, as sometime suggested