Structural study of the Sn/Ge interface of highly milled Sn-Ge powders.

Abstract

Structural changes occurring at the Sn/Ge interface of highly milled Sn-Ge powders were examined using extended x-ray-absorption fine-structure spectroscopy (EXAFS). X-ray diffraction and differential scanning calorimetry were also used as supporting techniques. Samples of varying compositions were prepared for analysis. Systematic changes in EXAFS and x-ray diffraction are observed with decreasing Sn concentration. These changes are found to be due to the fact that Sn appears in two different states, i.e., the metallic phase and an \ensuremath{\alpha}-Sn/Ge alloy phase several monolayers thick that forms at the Sn/Ge interface. When the Sn concentration is 20 vol % the alloy phase becomes the dominant phase, leaving essentially no Sn in the normal \ensuremath{\beta}-Sn phase. The results can be used to explain previously observed reductions in melting enthalpy and a low-temperature tail in the melting transition. The thermal stability of the alloy above the melting point of bulk Sn accounts for the reduction in melting enthalpy of Sn, and residual small Sn particles are the likely cause for the low-temperature tail in melting.