Pressure-induced structural transformations in phosphorus oxynitride glasses

Abstract The structure-property relations of permanently densified sodium metaphosphate oxynitride glasses (NaPO 3 − 3x/2 N x ) with varying N/P ratio are investigated. Densification of the bulk samples is achieved through 1 GPa isostatic compression at the glass transition temperature. The pressure-induced structural transformations are characterized by Raman spectroscopy and solid state 31 P and 23 Na NMR spectroscopy, whereas the glass hardness and brittleness are quantified through Vickers indentation. Nitridation of the ambient pressure sodium metaphosphate glass (NaPO 3 ) results in a step-wise conversion of PO 4 units into PO 3 N and PO 2 N 2 oxynitride species. Upon hot compression, the glasses become permanently denser and harder, but also more brittle. This pressure-induced densification is not accompanied by changes in the types or fractions of the structural units for the NaPO 3 glass. In contrast, densification of the oxynitride glasses (N/P > 0) is accompanied by pressure-induced structural transformations between the oxynitride species. Based on the 31 P NMR results, a structural mechanism for these transformations is proposed.