The effects of Sb on the thermoelectric properties of Mg₂Si_1−xGe_x prepared by using solid-state synthesis

Abstract

Sb-doped Mg₂Si_1−xGe_x solid solutions were successfully prepared by using a solid-state reaction and hot pressing. In the case of the undoped Mg₂Si_1−xGe_x specimens, the electrical conduction changed from n-type to p-type at room temperature for x ≥ 0.7 due to the intrinsic properties of Mg₂Ge. The electrical conductivity rapidly increased with increasing temperature, indicating a non-degenerate semiconducting behavior, and decreased with increasing Ge content. However, the Sb-doped Mg₂Si_1−xGe_x specimens showed n-type conduction, and the carrier concentration was increased from 4.0 × 10¹⁷ to 3.2 × 10²¹ cm⁻³ by doping with Sb atoms, which acted as donors. The absolute value of the Seebeck coefficient increased with increasing temperature, and the Seebeck coefficient ranged from −131 to −259 μV/K for the Sb-doped specimens. Sb doping reduced the thermal conductivities of the Mg₂Si_1−xGe_x solid solutions at temperatures above 723 K. Mg₂Si_0.5Ge_0.5:Sb_0.02 exhibited a maximum dimensionless figure-of-merit of 0.56 at 823 K.