SnO-containing oxynitride phosphate glasses have been obtained by ammonolysis and their structure studied by nuclear magnetic resonance. The nitrided glasses are characterized by tetrahedral units P(O,N)4 in which nitrogen atoms have substituted both bridging and non-bridging oxygen atoms. The N/O substitution in the anionic network induces important changes in the glass properties such as an increase in the glass transition temperature and a decrease in the coefficient of thermal expansion. 31P MAS NMR shows that PO4, PO3N and PO2N2 units coexist within the vitreous network and their relative proportions are a function of the nitrogen content as well as of the base glass composition. The influence of the different modifiers on the nitridation process is explained through a comparative study of the LiNaSnPON and LiNaPbPON systems. Unlike lead in oxynitride glasses, tin affects the nitridation mechanism by limiting the nitrogen/oxygen substitution in the anionic network, so that the substitution model is assumed to be closer to the one taking place in alkali phosphate glasses LiNaPON.

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