Hot Extruded Polycrystalline Mg 2 Si with Embedded XS 2 Nano-particles (X: Mo, W) A. BERCEGOL, 1,4 V. CHRISTOPHE, 2,3 M.K. KESHAVARZ, 2 D. VASILEVSKIY, 2 S. TURENNE, 2 and R.A. MASUT 1 1.—De ´partement de ge ´nie physique, Polytechnique Montre ´al, P.O. 6079, Succ. Centre-ville, Montreal H3C 3A7, Canada. 2.—De ´partement de ge ´nie me ´canique, Polytechnique Montre ´al, P.O. 6079, Succ. Centre-ville, Montreal H3C 3A7, Canada. 3.—E ´ cole Polytechnique, Route de Saclay, 91120 Palaiseau, France. 4.—e-mail: adrien.bercegol@polymtl.ca Due to their abundant, inexpensive and non-toxic constituent elements, magnesium silicide and related alloys are attractive for large-scale thermo- electric (TE) applications in the 500–800 K temperature range, in particular for energy conversion. In this work, we propose a hot extrusion method favorable for large-scale production, where the starting materials (Mg 2 Si and XS 2 , X: W, Mo) are milled together in a sealed vial. The MoS 2 nano-particles (0.5–2 at.%) act as solid lubricant during the extrusion process, thus facili- tating material densification, as confirmed by density measurements based on Archimedes’ method. Scanning electron microscopy images of bulk extruded specimens show a wide distribution of grain size, covering the range from 0.1 lm to 10 lm, and energy dispersive spectroscopy shows oxygen preferentially distributed at the grain boundaries. X-ray diffraction analysis shows that the major phase is the expected cubic structure of Mg 2 Si. The TE properties of these extruded alloys have been measured by the Harman method between 300 K and 700 K. Resistivity values at 700 K vary between 370 lX m and 530 lX m. The ZT value reaches a maximum of 0.26 for a sample with 2 at.% MoS 2 . Heat conductivity is reduced for extruded samples containing MoS 2 , which most likely behave as scattering centers for phonons. The reason why the WS 2 particles do not bring any enhancement, for either densification or heat transfer reduction, might be linked to their tendency to agglomerate. These results open the way for further investigation to optimize the processing parameters for this family of TE alloys. Key words: Magnesium silicide (Mg2Si), extrusion, heat transfer reduction, molybdenum disulfide (MoS 2 ) nano-particles, oxidation INTRODUCTION Harvesting the lost thermal energy after any combustion process appears to be a necessity, as steady progress is made towards energy-efficient design. Thermoelectric devices can be well adapted to this purpose if their overall efficiencies are increased. This will require that thermoelectric (TE) materials increase their Seebeck coefficient (a) as well as their electrical conductivity (r) while decreasing their thermal conductivity (k) resulting in a high figure-of-merit (ZT = a 2 rT/k). Several classes of thermoelectric materials are being inves- tigated for renewable power generation applications including tellurides, 1–3 half-Heuslers, 4–6 silicides 7 and skutterudites. Magnesium silicide (Mg 2 Si) and its alloys have lately been attracting attention because of the abundance and low price of their main constituent elements, as well as their low weight and non- toxicity. The binary compound of this TE material is a semi-conductor with indirect bandgap of 0.78 eV, recognized for possible applications in the (Received June 7, 2016; accepted August 9, 2016) Journal of ELECTRONIC MATERIALS DOI: 10.1007/s11664-016-4868-8 Ó 2016 The Minerals, Metals & Materials Society