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

Phosphates, as alum inosilicates, are a major family of glasses characteriz ed by XO4 tetrahedral units, in which nitrogen can substitute for oxygen, t hus forming oxynitride glasses. As shown by X-ray photoelectron spectroscop y (XPS), nitrogen N3- may exist in P(O, N)(4) tetrahedra as doubly coordina ted (-N=) and triply coordinated (-N <) atoms, respectively, bonded to two and three phosphorus atoms. They replace non-bridging (O=P) as well as brid ging (P-O-P) oxygen atoms, thus inducing a more covalent and cross-linked s tructure, and a correlation is observed between the O-1s and N-1s spectra. P-31 magic angle spinning nuclear magnetic resonance (MAS NMR) results show that three kinds of tetrahedra, PO4, PO3N and PO2N2, coexist within the gl ass network. The thermal nitridation in flowing ammonia of alkali metaphosp hate glasses is particularly studied here and a comparative XPS and NMR str uctural analysis of 'NaPON' and 'LiNaPON' phosphorus oxynitride glass serie s of increasing nitrogen content is presented. (C) 2001 Elsevier Science B. V. All rights reserved.