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

The crystalline structure and microstructure of some phases of the pseudo-b inary system AlN-Al2O3 are discussed, with special attention to the gamma s pinel phase. Samples with AlN content ranging between 43.3 and 3.5 mol % we re studied after different thermal treatments X-ray and neutron diffraction Rietveld peak-profile refinement allowed the determination of the cell par ameters and weight fraction of the phases. By checking different hypotheses of structure, it has been shown that the positions of the anions in the ga mma-AlON spinel phase are not ideal and correspond to a deformed face-centr ed cubic (f.c.c.) structure. This deviation is not due to the presence of v acancies in the cationic sublattice. The vacancies are distributed in the o ctahedral sites.