Nitridation of alkali metaphosphate glasses: a comparative structural analysis of the Na–P–O–N and Li–Na–P–O–N systems

Phosphates, as aluminosilicates, are a major family of glasses characterized by XO 4 tetrahedral units, in which nitrogen can substitute for oxygen, thus forming oxynitride glasses. As shown by X-ray photoelectron spectroscopy (XPS), nitrogen N 3 may exist in P(O, N) 4 tetrahedra as doubly coordinated (-N=) and triply coordinated (-N<) atoms, respectively, bonded to two and three phosphorus atoms. They replace non-bridging (O=P) as well as bridging (P-O-P) oxygen atoms, thus inducing a more covalent and cross-linked structure, and a correlation is observed between the O 1s and N 1s spectra. 31 P magic angle spinning nuclear magnetic resonance (MAS NMR) results show that three kinds of tetrahedra, PO 4 , PO 3 N and PO 2 N 2 , coexist within the glass network. The thermal nitridation in flowing ammonia of alkali metaphosphate glasses is particularly studied here and a comparative XPS and NMR structural analysis of NaPON' and LiNaPON' phosphorus oxynitride glass series of increasing nitrogen content is presented.