Glass samples were investigated by using normal-mode analysis, and the source of 2 distinct time-scales which had been observed by means of nuclear magnetic resonance techniques. It was shown that the normal-mode analyses gave results which were consistent with molecular dynamics simulations. Both methods furnished a consistent explanation for the origin of the nuclear magnetic resonance data. The existence of the 2 time-scales was attributed to a difference in mobility between two classes of fluoride ion. These were bridging fluoride and non-bridging fluoride ions. The difference in mobility became significant only below the glass transition temperature. Further analyses characterized the conduction mechanism more fully, via the use of normal-mode excitations. An important finding was that an activation process became important for bridging fluoride conduction below the glass transition temperature, whereas no equivalent process was observed for non-bridging fluoride ions.

R.Yamamoto, M.Kano, Y.Kawamoto: Journal of Physics - Condensed Matter, 1997, 9[24], 5157-66