Microscopic and thermodynamic interpretations of experimental data on ionic conductivity in lithium silicate glasses

Abstract

Experimental data on electrical conductivity are presented for 43 glass compositions in the xLi2O.(1-x)SiO2 system (0.05 < x < 0.67). The data are presented herein as a function of temperature and in isothermal plots as a function of the Li2O molar ratio x. Below Tg, the experimental ionic conductivity of all the compositions follows an Arrhenius law, sigma=sigma0exp(-EA/RT). The large quantity of experimental data minimizes the experimental inaccuracy in glass composition and conductivity measurements, thus allowing for accurate estimates of the mean values of the pre-exponential term (sigma0) of the Arrhenius expression and the activation energy (EA), as well as a precise assessment of the variations in isothermal conductivity with the molar ratio, x. The value of the pre-exponential term and the variation of isothermal conductivity and activation energy with x are then interpreted by reference to general concepts for ionic transport in solids, and to the so-called weak electrolyte theory. The Anderson and Stuart model is employed to estimate the absolute values of activation energy. The association of the intrinsic cationic pair model and the weak electrolyte theory provides a good description of the variations in electrical conductivity and activation energy as a function of the Li2O molar ratio. The Anderson and Stuart model leads to consistent absolute values of activation energy only if an arbitrarily chosen value of jump distance is employed in the corresponding expression