Ultrafast Combustion Synthesis and High Thermoelectric Performance of Mg3Sb2-x Bi x -Based Compounds

Mg3Sb2-based materials show great potential in the application of low temperature region power generation due to their excellent thermoelectric performance. However, the volatility and high vapor pressure of the Mg element make the synthesis of single-phase Mg3Sb2-based compounds with precisely controlled composition a real challenge especially by time- and energy-consuming traditional preparation methods, including the solid-state reaction and ball milling, which limits its application. Herein, we reported that single-phase Mg3Sb2-based compounds were successfully prepared by the self-propagating high-temperature synthesis (SHS) method for the first time. During the SHS process, the Mg element reacts with Sb directly forming the Mg3Sb2 compound. Alloying Mg3Bi2 in the Mg3Sb2-xBix system alters the chemical reaction process in the combustion process, where the Mg element reacts with Sb to form Mg3Sb2 and the as-formed Mg3Sb2 reacts with Mg and Bi to form Mg3Sb2-xBix (0 < x < 0.5) solid solution. Moreover, alloying Mg3Bi2 in the Mg3Sb2-xBix system lowers the combustion temperature and slows down the propagating speed of the combustion wave. The nonequilibrium structure formed during the ultrafast synthesis process leads to excellent thermoelectric performance and robust mechanical properties. The maximum ZT value of the Mg3Sb1.495Bi0.495Te0.01 sample reaches 0.92 at 723 K, and compressive strength, bending strength, and Vickers hardness are 337.5, 161.8, and 761.3 MPa, respectively. It lays a very strong foundation for the industrialized preparation and commercial application of Mg3Sb2-based high-performance thermoelectric materials.