Diffusion and correlation effects in iron-doped CoO

The diffusion of ⁵⁹Fe and ⁶⁰Co has been measured in pure CoO and dilute iron-doped CoO, (Co_1?cFe_cO, as a function of temperature (1000–1400°C) and oxygen partial pressure P_{o2), (10^?7 ≦ Po2 ≦ 0 21 atm) The enhancement factors for the diffusivities of iron and cobalt are nearly identical, which suggests that the primary cause of the enhancement is the increased concentration of charge-compensating cation vacancies with the addition of iron. The Fe ions dissolved in CoO appear to exist as a mixture of Fe²⁺ and Fe³⁺ ions, the fraction of iron ions in the three-plus state decreases with decreasing Po2 The simultaneous diffusion of ⁵²Fe and ⁵⁹Fe has been measured as a function of (itpo; at 1200°C The correlation factor for Fe impurity diffusion determined from the isotope-effect measurements is about the same as that for self-diffusion in CoO at high (itPo2} (2 × 10^?3 ≦ p_o2 ≦ 0 21 atm), but increases slightly with decreasing p_O2 Both the enhancement-effect and isotope-effect experiments suggest that the nearestneighbor interactions between Fe ions and vacancies is small, and that the dissolved Fe ions do not have strongly bound electron holes.