Abstract
In this study, the structure of mixed alkali nitrided phosphate glasses ‘LiNaPON’, of composition Li 0.5 Na 0.5 PO 3−3x/2 N x (0<x⩽0.55) , was investigated using X-ray photoelectron spectroscopy (XPS), 31P magic angle spinning (MAS) and double quantum (DQ) nuclear magnetic resonance (NMR) spectroscopies. XPS results show that nitrogen N 3− exists as two-coordinated –N atoms and three-coordinated –N atoms, respectively bonded to two and three phosphorus atoms, thus forming mixed PO 3N and PO 2N 2 tetrahedra. Nitrogen atoms substitute for bridging –O– as well as non-bridging O oxygen atoms and a correlation was observed between the O 1s and N 1s spectra. 31P MAS NMR results show that PO 4, PO 3N and PO 2N 2 tetrahedra coexist within the glass network. From our 31P 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 PO 4 and a PO 3N tetrahedron. Consequently, oxynitride micro-domains grow at the expense of oxygenated areas in such a way that connectivity between PO 4 tetrahedra is retained, even for the most nitrogen-rich glass compositions. Our data demonstrate that the nitrogen substitution for oxygen is not random.
Published Version
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