Thermoelectric Properties of Directionally Solidified Ag-Doped Mg3Sb2 Alloys

Mg3Sb2 crystals were successfully prepared by directional solidification method. The critical velocity of planar interface of single-phase Mg3Sb2 crystal was predicted according to the solidification theory, and the precipitated Sb phase can be inhibited below this rate. Microstructure analysis of Mg3Sb2 crystals at different solidification rates indicates that, the quantity of Mg vacancies can be effectively reduced. The excess Mg atoms in the crystals is conducive to the improvement of thermoelectric performance. Carrier mobility and concentration of Mg3Sb2 crystal is increased by grain boundary eliminated and Ag doping. On the premise of keeping a high Seebeck coefficient, the maximum electric conductivity is 309 S center dot cm(-1) at the testing temperature range of 300-800 K. As a result, a better electronic transport properties of PF=1.2 mW center dot m(-1)center dot K-2 is obtained. This result is verified by Hall testing and first-principle calculations. Correspondingly, the maximum ZT value is 0.67 at the doping concentration of 25at%. This method developed in this research provides a new path for the performance optimization of Mg3Sb2-based thermoelectric materials, and also provides a reference for the preparation of high-performance ternary Mg-3(Sb, Bi)(2) alloy.