Surface-doping of Cr2O3 particles by the 119Sn Mِssbauer probe: Influence of the gaseous environment on the dopant distribution

Chromium sesquioxide with 119Sn(II) dopant cations located just at the solid-gas interface (in the topmost cationic layer of the crystallites) has previously been synthesized by thermal treatment, under hydrogen flow, of Sn(IV) bulk-doped hydrated amorphous Cr(III) oxide. After exposure of the resulting Sn(II)/Cr2O3 material to various reactive gases, the probe environment was studied using Mِssbauer spectroscopy. The present work reports synthesis of Sn(II)/Cr2O3 under argon atmosphere, instead of hydrogen, which could modify the probe behavior in reactivity experiments. In addition, it shows that migration of the dopant from the bulk towards the surface of the crystallites depends upon the ability of the synthesis atmosphere to act as an electron donor for the oxide matrix. After exposure of these Sn(II)/Cr2O3 samples to chlorine, the 119Sn probe environment is found to be the same as for Sn(II)/Cr2O3 prepared under hydrogen, which excludes HCl involvement in the surface rearrangement process evidenced by previous Mِssbauer investigations.