The single-phase region of AlON, a spinel type solid solution in the system Al2O3-AlN, has been determined. AlON was synthesized from solid phase reactions between Al2O3 and AlN powder in several reaction vessels. The reaction vessel of porous Al2O3 with AlN coating was suitable for obtaining pure AlON. The single-phase region of AlON was from 28 to 32mol% AlN at 1700°C and from 20 to 34mol% AlN at 1800°C. The lattice parameters of AlON increased from 7.926 to 7.946Å with increasing AlN content. Y2O3-powder was used as a sintering aid to obtain translucent AlON from synthesized AlON powder at low temperature. For 1wt% Y2O3 addition, the translucent AlON was obtained at 1800°C, and its relative density and flexural strength were 99% and 250MPa, respectively.
