A MOSSBAUER-SPECTROSCOPY STUDY OF NANOSCALE GE-SN DISPERSIONS PREPARED BY BALL MILLING

Nanoscale mixtures of Ge/Sn, a nominally immiscible binary system, prepare mechanical attrition have been studied by Sn-119 Mossbauer spectroscopy. The Mossbauer measurements in general reveal two sites for the Sn atoms, a tetragonal beta-Sn site and another site designated as "A". The beta-Sn integrated intensity decreases in magnitude with Ge concentration, 1 - x, in Ge1-xSnx 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 Mossbauer spectroscopy at Sn-poor concentrations (x less-than-or-equal-to 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.