Abstract: Mg3Sb2-based alloy has become one of the most potential medium temperature thermoelectric materials due to its extremely low lattice thermal conductivity. However, its low carrier concentration and electrical conductivity are urgent problems to be solved. In addition to the doping, appearance of Mg vacancy is conducive to the p-type conduction tendency. Therefore, it is excepted to optimize the electronic transport performance by introducing Mg vacancy. Based on this, defect formation energy and electronic structures of Mg3Sb2 alloys with different sites and contents of Mg vacancy were calculated by use of first-principles calculations. It is determined that Mg1 sites tend to form a vacancy, and the maximum content of Mg vacancy is 0.05. The presence of Mg vacancy is also conducive to the shifting of the Fermi level to the valence band, which greatly increases the carrier concentration. Mg3Sb2 alloys with different contents of Mg vacancy were prepared by directional solidification method, and their thermoelectric property parameters were tested. The variation trend of electronic transport properties was consistent with the predicted results. The top values of electrical conductivity and power factor for Mg2.975Sb2 alloy are 110 S·cm-1 and 1.89 W·m-1·K-1, respectively. In addition, point defects caused by Mg vacancy are also conducive to the scattering of phonon and the reduction of lattice thermal conductivity. This results in an optimized figure of merit value of 0.49 for Mg2.975Sb2 alloy at T = 780 K. In this work, electronic transport property parameters of p-type Mg3Sb2 alloys were improved by regulating the Mg vacancy, and a new idea is provided for the thermoelectric performance optimization of Mg3Sb2-based alloys.
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2024, Vol. 38 
