Porous Mg₂(SiSn) thermoelectric composite with ultra-low thermal conductivity in submillimeter scale

Thermoelectric materials have attracted considerable attention in recent decades due to their thermal energy conversion. Suppression of the thermal conductivity and enhancement of the figure of merit (ZT) can be achieved through porosity and nanoengineering. This paper reports the fabrication of compact and porous Mg₂(SiSn) flakes in the submillimeter scale without conventional hot-pressing and spark plasma sintering process. X-ray diffraction measurements were performed to identify the chemical composition, and the thermoelectric properties of both samples were measured. The porosity induced more than 98% decrease in the phonon thermal conductivity. The effectiveness of the phonon scattering was significantly enhanced by the porous structure to lower the defect-induced phonon scattering time and phonon thermal conductivity. Despite the increase in electrical resistivity, the ultra-low thermal conductivity of the fabricated porous Mg₂(SiSn) resulted in a distinct fivefold enhancement of ZT. This approach provides experimental evidence of phonon scattering by structural porosity and a feasible route to synthesize thermoelectric Mg₂(SiSn) composites. Graphical abstract: [Figure not available: see fulltext.].