ROLE OF NITRIDES IN OXYNITRIDE GLASSES AND GLASS-CERAMICS - AN NMR INVESTIGATION

Crystallization of nitrogen-containing glasses based on the Li2O-Al2O3 -SiO2 system produces materials comprised of beta-quartz(ss) and beta- spodumene(ss), with minor amounts of X-phase (Si3Al6O12N2) and silicon oxynitride (Si2N2O). X-ray diffraction and Si-29 and Al-27 magic-angl e spinning NMR spectroscopy have been used to study the effect of nitr ogen on the thermal stability and atomic distribution of beta-quartz(s s), to monitor the evolution of secondary phases in the Li-Si-Al-O-N s ystem, and to compare the differences between using Si3N4 and AlN as t he nitrogen source. Samples containing less than or equal to 4wt % nit rogen and heat-treated at temperatures up to 1300 degrees C were analy zed by XRD to determine their crystallinity and phase content, whereas NMR was able to more clearly elucidate the atomic coordination and Si , Al distribution in the crystal structure.