High-Frequency Conductivity Plateau and Ionic Hopping Processes in a Ternary Lithium Borate Glass

Abstract

Complete conductivity spectra of a lithium ion conducting glass of composition B2O3-0.56Li2O-0.45 LiBr have been taken at twelve temperatures from 173 K to 573 K, covering the frequency range from a few Hertz up to about 50 THz. For the first time, a separation of the hopping and vibrational contributions to the spectra has been performed. The resulting frequency dependent hopping conductivity displays a high-frequency plateau similar to those known to exist in crystalline solid electrolytes like RbAg4I5 and Na-β-alumina. In the dispersive regime of the conductivity, there is an increase of the apparent power-law exponent from p = 0.6 to q= 1.3. The spectra are evaluated by combined application of the jump relaxation model and the dynamic structure model. Besides the translational hopping of the lithium ions via the preferred A sites, more localized kinds of motion are also detected, viz., hops into the less favoured C sites (and mostly back again) as well as smaller displacements of the ions within their local environment. © Verlag der Zeitschrift für Naturforschung