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

We report, for the first time, frequency-dependent conductivity spectra of glassy 0.1Li2O·0.1Na2O·0.1K2O·0.7B2O3 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 0.1Li2O·0.1Na2O·0.1K2O·0.7B2O3 are much lower than those of 0.3[xM2O·(1−x)Me2O]·0.7B2O3 (M–Me=Li–Na, Li–K, and Na–K) and 0.2[xLi2O·(1−x)Na2O]·0.8B2O3 glass systems, and the dc conductivity activation energy of glassy 0.1Li2O·0.1Na2O·0.1K2O·0.7B2O3 is higher than those of 0.3[xM2O·(1−x)Me2O]·0.7B2O3 and 0.2[xLi2O·(1−x)Na2O]·0.8B2O3 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.