29 Si, 27 Al and 15 N 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 β′-sialons (Si6 –z, AlzN8 –zOz; 0.1 < z < 2.7). The resulting 15N and 29Si 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 27Al 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.