Enhanced thermoelectric performance of bismuth-doped magnesium silicide synthesized under high pressure

Polycrystalline Mg₂Si_1−xBi _x compounds were prepared with high-pressure synthesis followed by spark plasma sintering. The structural and compositional analyses indicate a dominant antifluorite phase with the oxidation and volatilizing loss of Mg highly suppressed. High-pressure synthesis promotes Bi doping and the formation of interstitial Mg, both of which contribute electrons and give rise to high carrier concentration. Meanwhile, a relatively high carrier mobility is maintained with elevating carrier concentration, beneficial to the thermoelectric properties enhancement of our high-pressure synthesized samples. The optimal Mg₂Si_0.985Bi_0.015 possesses the highest power factor and the lowest thermal conductivity. As a result, the maximal ZT of 0.98 is achieved at 883 K, one of the highest values for the Bi-doped binary Mg₂Si compounds. Our results thus indicate the advantage of high pressure in synthesizing Mg₂Si-based thermoelectric materials with enhanced thermoelectric performance.