Structure property correlation in lithium borophosphate glasses

摘要

To investigate the influence of cation mobility variation due to the mixed glass former effect, 0.45Li_2O-(0.55 ? x)P_2O_5-xB2_O_3 glasses (0 ≤ x ≤ 0.55) are studied keeping the molar ratio of Li_2O/(P_2O_5 +B_2O_3) constant. Addition of B2O3 into lithium phosphate glasses increases the glass transition temperature (T_g) and number density, decreases the molar volume, and generally renders the glasses more fragile. The glass system has been characterised experimentally by XRD, XPS and impedance studies and studied computationally by constant volume molecular dynamics (MD) simulations and bond valence (BV) method to identify the structural variation with increasing the B_2O_3 content, its consequence for Li+ ion mobility, as well as the distribution of bridging and non-bridging oxygen atoms. These studies indicate the increase of P-O-B bonds (up to Y = [B_2O_3]/([B_2O_3] + [P_2O_5]) ≈ 0.5) and B-O-B bonds, as well as the decrease of P-O-P bonds and non-bridging oxygens (NBOs) with rising B_2O_3 content. The system with Y ≈ 0.5 exhibits maximum ionic conductivity, 1.0 × 10~(?7) Scm~(?1), with activation energy 0.63V. Findings are rationalised by a model of structure evolution with varying B_2O_3 content Y and an empirical model quantifying the effect of the various structural building blocks on the ionic conductivity in this mixed glass former system.