High-frequency dielectric properties of alkali and alkali-halide borate glasses

Time domain reflectometry (TDR) measurements have been carried out on glasses of compositions (B2O3)1-x(Li2O)x and (B2O3)1-x-y(Li2O)x(Li2Cl2)y. Dielectric spectra have been obtained in the frequency range of 5 MHz to 10 GHz and in temperature intervals from room temperature up to values in the vicinity of the glass temperatures. The dc conductivity results indicate that the presence of non-bridging oxygen atoms plays an important role in the diffusion of the mobile Li+ ions by means of the formation of clusters, which start to percolate at an Li2O concentration x almost-equal-to 0.4. The dc results of the glasses containing Li2Cl2 can be described well by an empirical concentration and temperature dependent power law. The analysis of the spectra in terms of the universal dynamic response, sigma(omega) = sigma0 + aomega(s), indicates that the conductivity exponent, s, is a function of both temperature and composition. We have observed that the exponent s is lower for samples showing higher conductivity values.