Semi-coherent zirconia inclusions in a ceramic matrix

Nanocomposite ceramic materials were fabricated by conventional sintering o f composite powders obtained by sol-gel coating of submicron powders. The m icrostructure of these MgAl2O4-ZrO2 materials was studied by transmission e lectron microscopy. All zirconia grains were in the tetragonal phase. In ad dition, the intragranular zirconia crystals exhibited heteroepitaxial orien tation relationships with the surrounding spinel grains, (hkl)(zirconia)//( hkl)(spinel). Semi-coherent interfaces along {111} planes were observed by high-resolution microscopy. The transformation toward the orthorhombic or t he monoclinic phase retained the epitaxial relationships as far as possible . The presence of such heteroepitaxial intragranular crystals in sintered c eramic materials, which did not involve a melting stage, was attributed to the specificity of the material preparation process.