Thermoelectric performance of quaternary Mg2(1+x)Si0.2Ge0.1Sn0.7 (0.06 ≤ x ≤ 0.12) solid solutions with band convergence

The study of Mg2Si based thermoelectric materials has received widespread attention. In this research, quaternary Mg2(1+x)(Si0.2Ge0.1Sn0.7)0.99Sb0.01 (0.06≤x ≤ 0.12) solid solutions with an optimized Sb doping were prepared by B2O3 flux method combined with spark plasma sintering (SPS) technique. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured as a function of Mg excess between 300 K and 780 K. The electron concentration, electrical conductivity and lattice thermal conductivity increase while the Seebeck coefficient decreases with increasing magnesium excess content. The electron effective mass enhancement for x ≥ 0.08 suggests the conduction band convergence of Mg2Si0.2Ge0.1Sn0.7. Mg2.16(Si0.2Ge0.1Sn0.7)0.99Sb0.01 with a maximum dimensionless figure of merit of 0.94 at 780 K stand out as one of the best materials for intermediate temperature applications, providing a good nontoxic alternative to PbTe.