SI-29, AL-27 AND N-15 MAGIC-ANGLE SPINNING NUCLEAR-MAGNETIC-RESONANCE STUDY OF O'-SIALONS AND SOME RELATED PHASES

Magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy has been used to study the local structural details of O'-sialons with varying composition (Si2-xAlxN2-xO1 + x; 0.04 < x < 0.4) as well as of the sialon polytypoid 21R (SiAl6N6O2) and some beta'-sialons (Si6-zAlzN8-zOz; 0.1 < z < 2.7). The resulting N-15 Si-29 NMR spectra for the O'-sialons are interpreted in terms of isomorphous substitution, which leaves the chemical shift virtually unchanged throughout the whole range of solid solution. The Al-27 spectra, on the other hand, indicate the existence of a range of different Al-tetrahedra in the sialons. In a proposed structural model both Si- and Al-tetrahedra contain N as well as O, although there is likely to be a preference for forming Al-O bonds and Si-N bonds, rather than a totally random distribution of Si and Al atoms over the metal sites and of O and N over non-metal sites.