ELECTRON VIBRATION COUPLING IN A DYNAMIC FRACTAL - SUPERIONIC BORATE GLASSES

In this paper we present the results of a study of the effects of dynamical fractality on vibrational dynamics and electron-vibration coupling in AgI-doped borate glasses, namely the compounds (AgI)x(Ag2O-nB2O3)1-x, with n = 1 and x = 0.4, 0-55 and 0-65. The samples were studied by time-of-flight inelastic neutron scattering and by Raman scattering at several temperatures. Particular care was given to obtain a precise and reliable spectral density with both techniques in the low-frequency range, namely about 1 to about 80 cm-1. In this range, clear indications of fractality were obtained from the anomalous behaviour of the vibrational density g(N)(omega) of states obtained by neutron scattering. In the same region we also observed a scaling behaviour of the electron-vibration coupling function, obtained from the ratio of the Raman spectral density g(R)(omega) to the neutron spectral density. g(N)(omega) was found to be essentially independent of temperature, whereas g(R)(omega) featured significant changes in the region omega almost-equal-to 100 cm-1 and for omega less-than-or-similar-to 10 cm-1, as the temperature was varied between 100 and 288 K. The changes indicate a modification of the spectral dependence of electron-vibration coupling due to activation of Ag ion motion in the dynamically fractal structure of AgI dissolved in the borate matrix.