High Thermoelectric Properties in Mg₂Ge_0.25Sn_0.75−xSb_x Solid Solution

Abstract

Mg₂Sn-based solid solutions Mg₂Ge_0.25Sn_0.75−xSb_x (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 Mg₂Ge_0.25Sn_0.75 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 Mg₂Ge_0.25Sn_0.72Sb_0.03 at 573 K. The lowest thermal conductivity of 1.17 W m⁻¹ K⁻¹ was found in Mg₂Ge_0.25Sn_0.65Sb_0.1 at 473 K. The maximum ZT of 1.54 was obtained in Mg₂Ge_0.25Sn_0.68Sb_0.07 at 623 K. Compared with the value 0.03 for its parent alloy at the same temperature, this is a dramatic improvement.