Site distribution and hyperfine parameters of tin impurities in alpha manganese

Dilute alloys of 0.1-0.5 at.% of enriched Sn-119 in alpha manganese were tr ansformed to hydrides with hcp, fee and beta-Mn structures by exposure to p ressures of molecular hydrogen up to 3 GPa at elevated temperatures and sub sequent quenching to room temperature. The samples were then transformed ba ck to alpha-Mn(Sn) by hot extraction of the hydrogen at temperatures up to 400 degrees C. Sn-119 Mossbauer spectra taken after hydrogen extraction dif fered considerably from those taken before the hydrogen treatment. This obs ervation is interpreted by a strongly different distribution of Sn atoms ov er the four crystallographically inequivalent sites in the alpha-Mn structu re before and after the treatment. A quantitative evaluation of the Mossbau er spectra yields the hyperfine parameters of Sn-119 on all Mn sites and sh ows that the preferred tin site is the Mn-I position in the alpha-Mn struct ure. (C) 1999 Elsevier Science S.A. All rights reserved.