A combined 14N/27Al nuclear magnetic resonance and powder X-ray diffraction study of impurity phases in beta-sialon ceramics

Beta-sialons are ceramic phases occurring in the SiO(2)-Si(3)N(4)-AlN-Al(2)O(3) system. A series of samples with differing compositions has been investigated by magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy and powder X-ray diffraction (XRD). Although the constituent nitrogen nuclei occupy positions of low symmetry in the beta-sialon structure, 14N NMR spectra could be recorded for the samples examined. The origin of the 14N signal could be traced to the presence of an aluminium nitride (AlN) impurity phase with the help of 27Al NMR and XRD results. Similarly, the existence of Al(2)O(3) grains could be readily detected for a number of samples. Thus, the combination of 14N and 27Al NMR is shown to be an especially effective tool in identifying and characterizing impurity phases in sialon ceramics, complementing the results obtained from standard XRD analysis.