Effect of Li2SO4 on the structure of Li2OB2O3 glasses

Abstract Infrared reflectance and Raman spectroscopic measurements of x Li 2 SO 4 · (1- x )[ R Li 2 O · B 2 O 3 ] fast ionic conducting glass samples with R = 1 (metaborate), R = 2 (pyroborate) and 0 ≤ x ≤ 0.60 have been made. The SO 4 2− ions of slightly distorted T d symmetry are found to occupy interstitial positions in the glass network and to decrease the basicity of the Li + -hosting sites. Increasing Li 2 SO 4 content induces small structural changes to the depolymerized R = 2 glasses, but has a larger effect on the structure of the more covalently bonded R = 1 network. In this latter case, small additions of Li 2 SO 4 , up to x ≈ 0.05, induce the transformation of metaborate triangles into their isomeric tetrahedral species. Further increases of x lead to the reversal of this trend. The complex influence of Li 2 SO 4 on the metaborate network is observed in the irregular shape of the Li 2 SO 4 Li 2 OB 2 O 3 glass-forming range, as well as on the non-monotonic dependence of the activation energy for ion transport on x . The spectroscopic results are compatible with the formation of Li 2 SO 4 microdomains at large Li 2 SO 4 contents.