Nitrogen and fluorine anionic substitution in lithium phosphate glasses

Phosphate based glasses containing simultaneously fluorine and nitrogen in significant amounts have been prepared according to a new synthesis route described in this paper. The results obtained on glass series based on a 55Li2O·45P2O5 composition (mol %) allow, for the first time, the investigation of the effect of fluorine introduction on lithium phosphate and lithium phosphorous oxynitride glasses. New structural features, including the presence of an unreported fluorine site and a change in the Q2 groups/fluorinated species ratio which depends on the lithium fluoride content, were derived from 1D 19F and 31P solid state NMR essays. Distinction between pure phosphate and fluorinated phosphate groups was established using the 2D 31P{19F} CP-HETCOR experiments. The evolution of the glass structure was studied as a function of the lithium fluoride content. The study of the properties of these glasses showed an increase of the ionic conductivity and a decrease of the glass transition temperature due to the phosphate network depolymerisation when lithium fluoride is introduced in the formulation.