The effects of ion implantation of Al 2O 3 followed by thermal annealing in a reducing environment have been studied and compared with the results obtained by annealing in an oxidizing environment. For the case of implanted Fe, partially coherent crystalline precipitates are observed after annealing in an oxidizing environment, and evidence is presented that crystalline precipitates of a different nature also form during annealing in a reducing environment. The precipitates which form in an oxidizing annealing environment have a major channeling axis nearly aligned with the Al 2O 3 <0001> direction. These precipitates are tentatively identified as Fe 3O 4. Lattice damage recovery is also different in the two annealing environments.