29Si,27Al and15N magic-angle spinning nuclear magnetic resonance study of O′-sialons and some related phases

Abstract

Magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy has been used to study the local structural details of O′-sialons with varying composition (Si_{2 –x}Al_xN_{2 –x}O_{1 +x}; 0.04 < x < 0.4) as well as of the sialon polytypoid 21R (SiAl₆N₆O₂) and some β′-sialons (Si_{6 –z}, Al_zN_{8 –z}O_z; 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.