DEFECTS IN COO - PERTURBED-ANGULAR-CORRELATION SPECTROSCOPY OF EQUILIBRIUM AND FROZEN-IN DEFECTS

The perturbed angular correlation (PAC) method was applied to study in trinsic defects in polycrystalline CoO after implantation of radioacti ve In-111 or Cd-111m ions. Measurements were performed in the temperat ure range 300-1450K and under various oxygen partial pressures adjuste d via a CO-CO2 gas mixture. Well defined electric field gradients were observed below 900K near the Co/CoO phase boundary. In annealing expe riments above 1100 K, an influence of the oxygen activity on the PAC s pectra was detected which allowed identification of the defect complex es. In contrast with the In-111 probe implantation, no trapping of def ects occurred after implantation of the isovalent Cd-111m probes. This clearly demonstrates the importance of the probe's charge state in io nic compounds. The conditions are discussed under which point defects in thermal equilibrium can be observed via PAC. Point charge model cal culations were used to cross-check the assignments made for the struct ure of the proposed probe defect configurations and for a comparison w ith recent results for NiO.