Diffusion of O 18 in Fe 3O 4: An experimental approach to study the behavior of minority defects in oxides

Abstract

The self diffusion of oxygen in Fe 3O 4 has been studied at 1150 °C by means of an oxygen isotopic exchange method. The experimental value of the oxygen diffusion coefficient D O ∗ decreases with the oxygen partial pressure in a lower range up to about 10 −7 atm with a slope equal to − 1 2 , while at higher P O 2 it increases with a slope of about 1 6 . These results are attributed to a change in the nature of the defects in the oxygen sublattice. At low P O 2 , where the majority defects are iron interstitials, the prevailing oxygen defects are free oxygen vacancies. At high P O 2 , where the majority defects are cation vacancies, the observed slope supports the presence of clusters of metal vacancies with oxygen vacancies formed as a result of the Coulombic attractions. A general discussion of the properties of minority defects in oxides is also presented.