VIBRATIONAL, REORIENTATIONAL AND TRANSLATIONAL IONIC MOTION IN GLASS

The techniques of inelastic neutron scattering and high-frequency conductivity measurement have been employed to analyze the ion dynamics in the lithium-ion conducting glass B2O3 . 0.56Li2O . 0.45LiBr at various temperatures. The neutron scattering data are interpreted by superposition of four contributions corresponding to damped oscillations of four different ionic units. Frequency dependent ionic conductivities have been measured from 1 kHz up to 60 GHz. At first sight, the conductivity spectra sigma(omega) seem to conform with a omega1.0 power law valid in wide frequency ranges. However, close inspection shows that two surprisingly well defined processes are superimposed, featuring different activation energies and different power-law exponents. The latter are 0.67 and 1.30. The two processes are identified with translational jump diffusion (including jump relaxation) and a non-Debye localized reorientational motion of the ions within a given neighbourhood.