Effects of Al/Sb Double Doping on the Thermoelectric Properties of Mg2Si0.75Sn0.25

Abstract

Al/Sb double-doped Mg2Si0.75Sn0.25 materials were prepared by liquid–solid reaction synthesis and the hot-pressing technique. The effects of Al/Sb double doping on the thermoelectric properties were investigated at temperatures between room temperature and 900 K, and the resistivity and Hall coefficient were investigated at 80 K to 900 K. Al/Sb double-doped samples were found to be n-type semiconductors in the investigated temperature range. The absolute Seebeck coefficient (α), resistivity (ρ), and thermal conductivity (κ) for Al/Sb double-doped samples at room temperature were in the ranges of 152.5 μV K−1 to 109.2 μV K−1, 2.92 × 10−5 Ω m to 1.29 × 10−5 Ω m, and 2.50 W K−1 m−1 to 2.86 W K−1 m−1, respectively. The absolute values of α increased with increasing temperature up to a maximum, and decreased thereafter. This could be attributed to mixed carrier conduction in the intrinsic region. κ decreased linearly with increasing temperature to a minimum near the intrinsic region, then increased rapidly because of bipolar components. The highest ZT value measured was 0.94 at 850 K for Mg1.9975Al0.0025Si0.75Sn0.2425Sb0.0075. Sb doping was effective for enhancement of ZT, because of a remarkable increase in the carrier concentration. However, Al doping was almost ineffective for enhancing ZT.