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 hig h temperatures (up to 1400-degrees-C) as a function of oxygen partial pressure, p(O2). The experimental in situ spectra are characteristical ly affected by cation diffusion processes. The spectra have been decon voluted into the contributions from iron ions on tetrahedral and octah edral sites of the spinel structure of magnetite. From the observed is othermal p(O2) dependences of the spectral line shapes it is concluded that cationic dynamics at high p(O2) is dominated by vacancy diffusio n on the octahedral sublattice, while at low p(O2) interstitialcy proc esses involving tetrahedrally coordinated iron ions are dominant. Exch ange processes play only a minor role.