MOSSBAUER STUDY OF THE CHEMICAL BEHAVIOR OF TIN DOPANT ATOMS ON THE SURFACE OF CR2O3 MICROCRYSTALS - TRANSFORMATIONS INDUCED BY EXPOSURE TOAMBIENT ATMOSPHERE AFTER CONTACT WITH H2S

Appearance of a particular tin dopant ion distribution with respect to the surface of Cr2O3 substrate after H2S adsorption and subsequent ex posure of the sample to air at room temperature has been revealed usin g Sn-119 probe Mossbauer spectroscopy, The results obtained show that drastic changes occur in the chemical composition of the first cationi c layer of the substrate during H2S adsorption. The subsequent contact with air results in oxidation of both Sn2+ dopant ions and adsorbed H 2S molecules. The Sn4+ ions formed in the oversurface shell consisting of H2S oxidation products appear to be magnetically isolated to a lar ge extent from the substrate surface. However, after annealing under h ydrogen flow, instead of forming beta-Sn clusters, even the most isola ted Sn4+ ions are shown to recover their initial divalent state and to return surface sites similar to those occupied by Sn2+ ions prior to H2S exposure. (C) 1997 Academic Press.