Density and ultrasonic velocities in fast ionic conducting borate glasses

The density and the sound velocities have been measured at room temperature in the ternary borate glasses, B2O3−xLi2O−yLinX (n=1 for X=F, Cl, Br and I; and n=2 for X=SO4), as a function of the concentration for the different ‘doping’ salts (LinX). Two series of ternary glasses with different O/B ratios, x=0.2 and 0.6, have been studied. In both series, a structural model where the anion of the ‘doping’ salts are located in interstitial positions inside the boron–oxygen network is used to explain the experimental results in borate glasses ‘doped’ with LiCl, LiBr and LiI. In the case of glasses ‘doped’ by LiF or Li2SO4, there is evidence of a direct participation of the salt anions to the boron–oxygen network. A structural modification is proposed for the LiF-‘doped’ borate glasses with x=0.2 and 0.6. Changes in the medium-range order induced by the addition of ‘doping’ salts are also discussed in these ternary glasses.