Achieving a High in n-Type Sb-Doped MgSiSn via High-Pressure-Modulated Microstructures.

MgSi-based compounds are cost-effective and environmentally friendly thermoelectric materials. However, the current Mg(Si,Sn) solid solutions still suffer from the low figure of merit (or the low energy conversion efficiency), especially the low averaged value ( < 1.0). In this study, we synthesize the Mg(SiSn)Sb ( = 0, 0.5, 0.75, 1, and 1.5%) solid solutions through the combination of high-pressure, high-temperature (HPHT) synthesis and spark plasma sintering (SPS). The high-pressure instrument effectively inhibits the unfavorable oxidation of Mg. This HPHT + SPS methodology improves the defect formation efficiency of Sb-doped MgSiSn, leading to an increased carrier concentration and enhanced electrical conductivity. Moreover, as a benefit from the pressure-induced conduction band convergence and Sb-flattened conduction band, the density of states' effective mass (*) significantly increases to ∼3.3, maintaining high Seebeck coefficients even at a high carrier concentration. The synergetic effects of doping and * increase the peak power factor to exceed 50 μW cm K. Notably, due to the HPHT-modified microstructures, the hierarchy phonon scatterings are established to suppress the lattice thermal conductivity to as low as 1.29 W m K at 568 K; the Sb point defects, dislocations, and grain boundaries/pores can scatter the short-, medium-, and long-wavelength phonons, respectively. Ultimately, of the optimized Mg(SiSn)Sb sample increases significantly in the whole temperature region; the peak is 1.37 at 673 K, and a high plateau of ∼1.35 is realized between 568 and 723 K. Thus, the notable average over the range of 323-723 K is 1.08. Our work demonstrates that the high-pressure-induced defect concentration, effective doping, and microstructure modifications facilitate the thermoelectric property improvement in the Mg(Si,Sn)-based compounds.