High Thermoelectric Properties in Mg2Ge0.25Sn0.75−xSbx Solid Solution

Mg2Sn-based solid solutions Mg2Ge0.25Sn0.75−xSbx (x = 0, 0.03, 0.05, 0.07, 0.10, 0.15) were synthesized by high-frequency melting in a graphite crucible, followed by spark plasma sintering. The effects of Sb substitution on the phase constitution and thermoelectric properties of the solution were investigated. All the samples were face-centered cubic Mg2Ge0.25Sn0.75 solutions without any additional phase arising from Sb in the compounds. The electrical resistivity decreased significantly from 202 μΩ m to 3.66 μΩ m at 300 K as lower Sb content x increased from 0 to 0.03, but increased slightly from 3.66 μΩ m to 11.6 μΩ m at 300 K as Sb content x further increased from 0.03 to 0.15. The Seebeck coefficient showed a similar pattern of change. The thermal conductivity of the solid solution clearly decreased from 3.6 W m−1 K−1 to 1.4 W m−1 K−1 at 300 K as Sb content x increased from 0 to 0.15. The highest power factor of 4010 μW m−1 K−2 was obtained in the sample of Mg2Ge0.25Sn0.72Sb0.03 at 573 K. The lowest thermal conductivity of 1.17 W m−1 K−1 was found in Mg2Ge0.25Sn0.65Sb0.1 at 473 K. The maximum ZT of 1.54 was obtained in Mg2Ge0.25Sn0.68Sb0.07 at 623 K. Compared with the value 0.03 for its parent alloy at the same temperature, this is a dramatic improvement.