HIGH-FREQUENCY CONDUCTIVITY PLATEAU AND IONIC HOPPING PROCESSES IN A TERNARY LITHIUM BORATE GLASS

Complete conductivity spectra of a lithium ion conducting glass of com position B2O3-0.56 Li2O-0.45 LiBr have been taken at twelve temperatur es 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 an d vibrational contributions to the spectra has been performed. The res ulting frequency dependent hopping conductivity displays a high-freque ncy plateau similar to those known to exist in crystalline solid elect rolytes like RbAg4I5 and Na-beta-alumina. In the dispersive regime of the conductivity, there is an increase of the apparent power-law expon ent from p = 0.6 to q = 1.3. The spectra are evaluated by combined app lication of the jump relaxation model and the dynamic structure model. Besides the translational hopping of the lithium ions via the preferr ed ($) over bar A sites, more localized kinds of motion are also detec ted, viz., hops into the less favoured ($) over bar C sites (and mostl y back again) as well as smaller displacements of the ions within thei r local environment.