Self-diffusion was studied at 1150C by using an O isotopic exchange method. It was found that the O diffusion coefficient decreased with pressure, for O partial pressures of less than about 10-7atm, with a slope of ½. At higher O partial pressures, the O diffusion coefficient increased with pressure. These results were attributed to a change in the nature of the defects in the O sub-lattice. At low O partial pressures, where the main defects were Fe interstitials, the prevailing O defects were free O vacancies. At high O partial pressures, where the main defects were cation vacancies, the observed slope indicated the presence of clusters, of metal vacancies with O vacancies, that were due to Coulombic attraction.

F.Millot, N.Yan: Journal of the Physics and Chemistry of Solids, 1997, 58[1], 63-72