DISORDER AND DIFFUSIONAL MOTION OF CATIONS IN MAGNETITE, FE3-DELTA-O4, STUDIED BY MOSSBAUER-SPECTROSCOPY AT HIGH-TEMPERATURES

Mossbauer spectra of magnetite, Fe3-deltaO4, have been measured at high temperatures (up to 1400-degrees-C) as a function of oxygen partial pressure, p(O2). The experimental in situ spectra are characteristically affected by cation diffusion processes. The spectra have been deconvoluted into the contributions from iron ions on tetrahedral and octahedral sites of the spinel structure of magnetite. From the observed isothermal p(O2) dependences of the spectral line shapes it is concluded that cationic dynamics at high p(O2) is dominated by vacancy diffusion on the octahedral sublattice, while at low p(O2) interstitialcy processes involving tetrahedrally coordinated iron ions are dominant. Exchange processes play only a minor role.