Abstract

High-resolution ²⁹Si and ²⁷Al NMR spectra have been obtained from seven crystalline samples of lithium α-sialon with different compositions. The ²⁹Si isotropic chemical shift is found to be constant within the experimental error across the whole substitution range and its value, δ_Si ≈ −48 ppm, suggests that silicon remains largely in an SiN₄ coordination for all compositions. The ²⁷Al 1D MAS NMR spectra exhibit a range of tetrahedral coordinations AlO_xN_4 − x (x = 0–4), which vary as the aluminium and oxygen contents increase. The results are consistent with previous studies of sialons, which indicate that silicon prefers to be coordinated by nitrogen whereas aluminium prefers coordination by oxygen. Some NMR parameters are derived from two-dimensional ²⁷Al MQMAS spectra, including those for the resolved AlO₄ peak. However, it is shown that this technique does not allow the different aluminium tetrahedral mixed environments (AlO₃N, AlO₂N₂ and AlON₃) to be resolved.