Effect of Silicon Carbide Nanoparticles on the Grain Boundary Segregation and Thermoelectric Properties of Bismuth Doped Mg₂Si_0.7Ge_0.3

Abstract

The effect of silicon carbide (SiC) nanoparticles on the thermoelectric properties of Mg₂Si_0.676Ge_0.3Bi_0.024 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.