Mg9Si5: a potential non-toxic thermoelectric material for mid-temperature applications

Mid-temperature thermoelectric applications include waste heat recovery from automobile exhausts, various industrial process and solar thermoelectrics. The current systems that have been extensively investigated for mid-temperature applications are mostly tellurides. However, the low crustal abundance of tellurium contributes significantly to their price volatility which impedes their usage in commercial technology. Looking from the perspective of material cost effectiveness in terms of crustal abundance and environmental sustainability, we investigate the thermoelectric properties of Mg9Si5 systems, the constituents of which are geo-abundant and non-toxic. By means of first principles calculations, we find Mg9Si5 to be a potential mid-temperature thermoelectric material, with an operational temperature in the range of ≃400–600 K, depending on the exact carrier concentration. We also discuss the enhanced viability of substitution in Mg9Si5, a case that seems to be restricted in Mg2Si because of its chemically balanced Zintl nature.