Diffusion of O-18 in Fe3O4: An experimental approach to study the behavior of minority defects in oxides

The self diffusion of oxygen in Fe3O4 has been studied at 1150 degrees C by means of an oxygen isotopic exchange method. T The experimental value of the oxygen diffusion coefficient D-0* 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-O2 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-O2, where the majority defects are iron interstitials, the prevailing oxygen defects are free oxygen vacancies. At high P-O2, 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. (C) 1996 Elsevier Science Ltd.