Crystalline and microstructure study of the AlN–Al₂O₃ section in the Al–N–O system. I. Polytypes and γ-AlON spinel phase

The crystalline structure and microstructure of some phases of the pseudo-binary system AlN–Al₂O₃ are discussed, with special attention to the γ spinel phase. Samples with AlN content ranging between 43.3 and 3.5 mol % were studied after different thermal treatments. X-ray and neutron diffraction Rietveld peak-profile refinement allowed the determination of the cell parameters and weight fraction of the phases. By checking different hypotheses of structure, it has been shown that the positions of the anions in the γ-AlON spinel phase are not ideal and correspond to a deformed face-centred cubic (f.c.c.) structure. This deviation is not due to the presence of vacancies in the cationic sublattice. The vacancies are distributed in the octahedral sites.