Effect of Silicon Carbide Nanoparticles on the Grain Boundary Segregation and Thermoelectric Properties of Bismuth Doped Mg2Si0.7Ge0.3

The effect of silicon carbide (SiC) nanoparticles on the thermoelectric properties of Mg2Si0.676Ge0.3Bi0.024 was investigated. Increasing the concentration of SiC nanoparticles systematically reduces the electrical conductivity from 431 Ω−1 cm−1 for the pristine sample to 370 Ω−1 cm−1 for the sample with 1.5 wt.% SiC at 773 K, while enhancing the Seebeck coefficient from −202 μV K−1 to −215 μV K−1 at 773 K. In spite of the high thermal conductivity of SiC, its additions could successfully decrease the lattice thermal conductivity from 3.2 W m−1 K−1 to 2.7 W m−1 K−1 at 323 K, presumably by adding more interfaces. The Z contrast transmission electron microscopy imaging (Z = atomic number) and energy dispersive x-ray spectroscopy revealed bismuth segregation at the grain boundary. In summary, the figure of merit reached its maximum value of 0.75 at 773 K for the sample containing 0.5 wt.% SiC.