Validation of the mechanism of nitrogen/oxygen substitution in Li–Na–Pb–P–O–N oxynitride phosphate glasses

As evidenced by O1s X-ray photoelectron spectroscopy, there are three kinds of oxygen atoms in Li0.25Na0.25Pb0.25PO3 3x/2Nx oxynitride phosphate glasses (0 < x 6 0.67): (i) bridging oxygens (BO) which interconnect the P(O,N)4 tetrahedral units of the glass network (ii) non-bridging oxygens (NBO) which coordinate the modifier cations and (iii) oxygen atoms, also non-bridging, which belong to PO4 tetrahedra involved in the coordination sphere of Pb2+. The variation of their relative proportions as the nitrogen content increases is explained according to the nitridation mechanism previously proposed for this series of glasses. Moreover, the variation of the BO/NBO ratio confirms that the nitrogen/oxygen substitution taking place during nitridation obeys the simple chemical equivalences already stated