High efficiency Mg₂(Si,Sn)-based thermoelectric materials: scale-up synthesis, functional homogeneity, and thermal stability

Abstract

Considering the need for large quantities of high efficiency thermoelectric materials for industrial applications, a scalable synthesis method for high performance magnesium silicide based materials is proposed. The synthesis procedure consists of a melting step followed by high energy ball milling. All the materials synthesized <i>via</i> this method demonstrated not only high functional homogeneity but also high electrical conductivity and Seebeck coefficients of around 1000 Ω^-1 cm^-1 and -200 μV K^-1 at 773 K, respectively. The measured values were similar for all the samples extracted from the <i>∅</i>50 mm and <i>∅</i>70 mm compacted pellets and were stable upon thermal cycling. Thermal stability experiments from 168 hours to 720 hours at 723 K revealed no significant change in the material properties. The low thermal conductivity of ∼2.5 W m^-1 K^-1 at 773 K led to a maximum figure of merit, <i>zT</i> _max, of 1.3 at the same temperature and an average value, <i>zT</i> _avg, of 0.9 between 300 K and 773 K, which enables high efficiency in future silicide-based thermoelectric generators.