X-ray photoelectron spectroscopy and nuclear magnetic resonance structural study of phosphorus oxynitride glasses, 'LiNaPON'

In this study, the structure of mixed alkali nitrided phosphate glasses 'LiNaPON', of composition Li(0.5)Na(0.5)PO(3-3x/2)Nx (0 < x less than or equal to 0.55), was investigated using X-ray photoelectron spectroscopy (XPS), P-31 magic angle spinning (MAS) and double quantum (DQ) nuclear magnetic resonance (NMR) spectroscopies. XPS results show that nitrogen N3- exists as two-coordinated -N= atoms and three-coordinated -N drop atoms, respectively bonded to two and three phosphorus atoms, thus forming mixed PO3N and PO2N2 tetrahedra. Nitrogen atoms substitute for bridging -O- well as non-bridging = O oxygen atoms and a correlation was observed between the O-1s and N-1s spectra, P-31 MAS NMR results show that PO4, PO3N and PO2N2 tetrahedra coexist within the glass network. From our P-31 MAS and double quantum NMR results, we propose a model of nitrogen/oxygen substitution in which nitrogen atoms preferentially substitute for oxygen atoms shared by a PO4 and a PO3N tetrahedron. Consequently, oxynitride micro-domains grow at the expense of oxygenated areas in such a way that connectivity between PO4 tetrahedra is retained, even for the most nitrogen-rich glass compositions. Our data demonstrate that the nitrogen substitution for oxygen is not random. (C) 2000 Elsevier Science B.V, All rights reserved.