High figure of merit and thermoelectric properties of Bi-doped Mg2Si0.4Sn0.6 solid solutions

The study of Mg2Si1-xSnx-based thermoelectric materials has received widespread attention due to a potentially high thermoelectric performance, abundant raw materials, relatively low cost of modules, and non-toxic character of compounds. In this research, Mg-2.16(Si0.4Sn0.6)(1-y)Bi-y solid solutions with the nominal Bi content of 0 <= y <= 0.03 are prepared using a two-step solid state reaction followed by spark plasma sintering consolidation. Within this range of Bi concentrations, no evidence of second phase segregation was found. Bi is confirmed to occupy the Si/Sn sites in the crystal lattice and behaves as an efficient n-type dopant in Mg2Si0.4Sn0.6. Similar to the effect of Sb, Bi doping greatly increases the electron density and the power factor, and reduces the lattice thermal conductivity of Mg2.16Si0.4Sn0.6 solid solutions. Overall, the thermoelectric figure of merit of Bi-doped Mg2.16Si0.4Sn0.6 solid solutions is improved by about 10% in comparison to values obtained with Sb-doped materials of comparable dopant content. This improvement comes chiefly from a marginally higher Seebeck coefficient of Bi-doped solid solutions. The highest ZT similar to 1.4 is achieved for the y=0.03 composition at 800 K. (C) 2013 Elsevier Inc. All rights reserved.