A Mössbauer spectroscopy study of nanoscale Ge–Sn dispersions prepared by ball milling

Abstract

Nanoscale mixtures of Ge/Sn, a nominally immiscible binary system, prepared by mechanical attrition have been studied by ¹¹⁹Sn Mössbauer spectroscopy. The Mössbauer measurements in general reveal two sites for the Sn atoms, a tetragonal β–Sn site and another site designated as “A”. The β-Sn integrated intensity decreases in magnitude with Ge concentration, 1 – x, in Ge_1−xSn_x as the second A-site intensity increases. The isomer shift and the small/negligible quadrupole splitting of site A suggests it represents Sn in solid solution in the Ge lattice. This in turn represents a large (12–24 at. %) nonequilibrium solid solubility of Sn in Ge prepared by mechanical milling, compared to the equilibrium value of <1.0 at. %. Oxidation of the Sn was detected by Mössbauer spectroscopy at Sn-poor concentrations (x ⋚ 0.10) when the milling vial was not totally free of oxygen (i.e., milling in impure argon). This may be due to rapid oxidation of finely divided Sn film particles possessing a large surface-to-volume ratio at these compositions.