Defects in CoO Perturbed angular correlation spectroscopy of equilibrium and frozen-in defects

Abstract

Abstract The perturbed angular correlation (PAC) method was applied to study intrinsic defects in polycrystalline CoO after implantation of radioactive 111In or IIImCd ions. Measurements were performed in the temperature range 300–1450 K and under various oxygen partial pressures adjusted via a CO-CO2 gas mixture. Well defined electric field gradients were observed below 900 K near the Co/CoO phase boundary. In annealing experiments above 1100K, an influence of the oxygen activity on the PAC spectra was detected which allowed identification of the defect complexes. In contrast with the 111m Cd probes implantation, no trapping of defects occurred after implantation of the isovalent 111mCd probes. This clearly demonstrates the importance of the probe's charge state in ionic compounds. The conditions are discussed under which point defects in thermal equilibrium can be observed via PAC. Point charge model calculations were used to cross-check the assignments made for the structure of the proposed probe defec...