Ionic conductivity of glasses with two and three types of alkali ions

We report, for the first time, frequency-dependent conductivity spectra of glassy 0.1Li(2)O center dot 0.1Na(2)O center dot 0.1K(2)O center dot 0.7B(2)O(3) over a wide temperature range. The conductivity isotherms of the studied glasses show a transition from their dc plateaus into a dispersive regime where the conductivity continuously increases with frequency tending towards a linear frequency dependence at sufficiently low temperatures. At a given temperature, the dc conductivity values of glassy 0.1Li(2)O center dot 0.1Na(2)O center dot 0.1K(2)O center dot 0.7B(2)O(3) are much lower than those of 0.3[xM(2)O center dot (1-x)Me2O] center dot 0.7B(2)O(3) (M-Me=Li-Na, Li-K, and Na-K) and 0.2[xLi(2)O center dot (1-x)Na2O] center dot 0.8B(2)O(3) glass systems, and the dc conductivity activation energy of glassy 0.1Li(2)O center dot 0.1Na(2)O center dot 0.1K(2)O center dot 0.7B(2)O(3) is higher than those of 0.3[xM(2)O center dot (1-x)Me2O]- 0.7B(2)O(3) and 0.2[xLi(2)O center dot (1-x)Na2O] center dot 0.8B(2)O(3) glasses with x=0, 0.2, 0.4, 0.6, 0.8, and 1, respectively. The experimental results are interpreted in terms of the Dynamic Structure Model (DSM) developed by Bunde, Ingram, and Maass. On the basis of our results, we predict that mixed alkali glasses with three types of cations will show a stronger mixed alkali effect in physical quantities related to the ion transport than glasses with only two types of cations. (c) 2004 Elsevier B.V. All rights reserved.