Metal-ceramic microstructures were obtained by partial reduction of the spinel compound NiAl 2 O 4 . Electron microscopy studies were performed for microstructural characterization, phase identification and chemical analysis. Depending on the reduction temperature, two different morphologies of nearly pure Ni particles, equiaxed and rod-like, form within a ceramic matrix. The equiaxed Ni particles (0.02-0.5 μm in diameter) are embedded in α-Al 2 O 3 , while the rod-like Ni particles (~ 5 μm in length and ~ 0.1 μm in diameter) are in a metastable ''defect spinel'' containing much less Ni than NiAl 2 O 4 . The fracture toughness of the Ni Al 2 O 3 mixture was significantly improved with respect to that of the original spinel phase.