Microstructural rearrangement during vacancy annihilation in Co[sub 1] [minus][delta]O

When the equilibrium defect concentration of an oxide is lowered, the defects must become annihilated to obtain the lower equilibrium concentrations. Classical point defect theory states that this annihilation reaction must occur at a free surface. If the extent of the annihilation is large enough then structural rearrangement can occur at this free surface. Experiments of this type have been performed on the cation deficient oxides Ni[sub 1][minus][delta] and CO [sub 1][minus][delta]O where the equilibrium cation vacancy concentration was lowered by lowering the temperature and/or oxygen pressure of the system. These experiments showed that structural rearrangements occurred at the free surfaces of the oxides and that the type of rearrangement depended upon the manner in which the defect concentrations were lowered. The authors have also performed vacancy annihilation experiments on Co[sub 1][minus][delta]O, and this communication will show that their results are consistent with the previous investigations and that the microstructural rearrangement that takes place at the free surfaces of these oxides is very sensitive to the extent of the annihilation process.