The mixed glass former effect in twin-roller quenched lithium borophosphate glasses

A whole series of lithium borophosphate glasses of composition 45 Li2O–55 [x B2O3–(1 − x) P2O5], 0 ≤ x ≤ 1 was prepared for the first time, thanks to the use of the twin roller quenching technique. As their more popular sodium counterparts, these glasses exhibit a mixed glass former effect with non linear increase in both glass transition temperature and conductivity when phosphorous is replaced by boron. A fairly good conductivity (~ 2 × 10− 7 Ω− 1.cm− 1 at room temperature) coupled to a high Tg (~ 450 °C) makes these glasses interesting as solid electrolytes for the development of thin-film batteries. A structural investigation was carried out both by Raman spectroscopy and for the first time, by 11B NMR at high field, 18.8 T. Raman spectra showed the signature of many types of vibrations indicating the presence of a large variety of entities in the glasses. 11B NMR at 18.8 T helped in separating the resonances of three-coordinated and four-coordinated boron species and counting them by direct integration. On the whole it was shown that while the Tg evolution relied upon the presence of mixed borophosphate entities, the conductivity was directly linked to the presence of BO4 entities alone irrespective of their specific environment.