No abstract

The use of Mg 2 Si 0.6 Sn 0.4 under air in thermoelectric modules in the mid-temperature range of 400−600 °C is linked to its ability to resist oxidation. In this study, oxidation experiments performed at 400 °C under air evidenced the stability of the material, either under static conditions (up to 100 h) or under severe heating-cooling cyclic conditions (up to 400 cycles), showing its ability to be used in a reliable way at this temperature. By combining thermogravimetry, scanning electron microscopy, temperature X-ray diffraction analysis, and mechanical and thermodynamic considerations, a mechanism is proposed explaining how Mg 2 Si 0.6 Sn 0.4 further undergoes decomposition with time under air when treated above 500 °C. The presence of Sn and the formation of various oxides are the key parameters of the material's degradation.

A new ternary phase with a composition Al 1+x V 2 Sn 2-x (x=0.19) has been found during the investigation of the Al-V-Sn ternary system. Single crystal X-ray diffraction measurements reveal that this ternary phase crystallizes with an orthorhombic structure with a = 5.5931(1) Å, b = 18.8017(5) Å and c = 6.7005(2) Å (Space group Cmce). This compound is thus isostructural to the GaV 2 Sn 2 structure type, showing a layered structure composed of vanadium clusters band formed with pentagonal faces intercalated by tin atoms layer. High resolution transmission electron microscopy measurements confirm the orthorhombic structure. Regarding lattice perfection, no dislocation could be identified within the probed Al 1.19 V 2 Sn 1.81 single crystal lamella.Ab initio calculations reveal a reduction of the density of states at the Fermi level, which could be attributed to both a Hume Rothery effect combined with strong spd hybridization.