HOPPING IN A REARRANGING STRUCTURE

We discuss a simple model for the localized hopping of a charged parti cle in a rearranging structural environment, whose dynamics are descri bed by an overdamped Brownian motion. We find that the dipolar relaxat ion strongly depends on how the bare jump frequency nu of the particle and the characteristic structural relaxation time tau(s), of its envi ronment relate to each other. For nu tau(s) << 1 the imaginary part of the dielectric susceptibility chi''(omega) exhibits a single-peak pat tern, while for nu tau(s) greater than or similar to 1 a second smalle r peak appears at higher frequencies, which becomes more separated fro m the first peak with increasing nu tau(s). It is suggested that this behaviour provides an explanation for the decoupling phenomenon of sec ondary beta relaxations from the main primary alpha relaxations as is often observed close to a glass transition.