SPECTROSCOPIC INSITU INVESTIGATIONS OF SOLIDS AT HIGH-TEMPERATURES - A MOSSBAUER AND OPTICAL SPECTROSCOPY STUDY OF DIFFUSION AND OF THE KINETICS OF SOLID-STATE REACTIONS

We report on Mössbauer and on optical in situ investigations of diffusion dynamics and of solid state reaction kinetics. The first example refers to the cation diffusion in magnetite, Fe3-δO4. From the isothermal oxygen activity dependence of the Mössbauer spectra detailed information is deduced on cation diffusion taking place on the two regular cation sublattices of the spinel structure. The second example concerns the homogeneous disorder reaction establishing cation distributions in spinels. Our results obtained from optically detected temperature-jump experiments indicate surprisingly rapid kinetics for this reequilibration process in CoAl2O4 and NiAl2O4 at high temperatures. Finally, results are reported of a Mössbauer high-temperature investigation of the internal oxidation reaction in the system Mg-Fe-O induced by rapid changes in oxygen activity. © 1990.