Dielectric and dynamic mechanical study of ionic motions in a ZrF 4-based fluoride glass

Abstract

The dielectric permittivity and loss of 0.55 ZrF 4 -0.31BaF 2 -0.06NaF-0.05LaF 3 -0.03AlF 3 glass were measured from 12 Hz to 100 kHz over a wide temperature range up to its T g . Its dynamic mechanical properties were measured from 10 −3 to 1 Hz and at 3 kHz. The dielectric and mechanical relaxation spectra have nearly the same half-width and are much narrower than those observed for other amorphous solids. The rate of the mechanical relaxation is the same as of the electrical relaxation and the two have the same temperature dependence. An analysis for the origin of the two relaxations in terms of the structure of the glass suggests that loosely packed local regions where molecular motion persists may involve regions of unbridged fluoride ions and that the introduction of Ba or other ions in the matrix is partly responsible for the greater strength of the relaxations, while dc conduction in them may still involve long-range diffusion of F − ions.