MgO and Co1−xO powders in 9:1 and 1:9 molar ratio (denoted as M9C1 and M1C9, respectively) were sintered and homogenized at 1600C followed by annealing at 850 and 800C, respectively to form defect clusters and precipitates. Analytical electron microscopic observations indicated the protoxide remained as rock salt structure with complicated planar diffraction contrast for M9C sample, however with spinel paracrystal precipitated from the MC9 sample due to the assembly of charge- and volume-compensating defects of the 4:1 type, i.e., 4 octahedral vacant sites surrounding one Co3+-filled tetrahedral interstitial site. The spacing of such defect clusters was 4.5 times the lattice spacing of the average spinel structure of Mg-doped Co3−δO4, indicating a higher defect cluster concentration than undoped Co3−δO4. The {111} faulting of Mg-doped Co3−δO4/Co1−xO in the annealed M1C9 sample implied the possible presence of zinc blend-type defect clusters with cation vacancies assembled along O close-packed (111) plane.

Defect Clusters and Precipitation/Oxidation of MgO–Co1-xO Solid Solution. T.M.Tsai, K.C.Yang, P.Shen: Journal of Solid State Chemistry, 2004, 177[10], 3301-9