Extraordinary n-Type Mg3 SbBi Thermoelectrics Enabled by Yttrium Doping.

Advancing thermoelectric n-type Mg3 Sb2 alloys requires both high carrier concentration offered by effective doping and high carrier mobility enabled by large grains. Existing research usually involves chalcogen doping on the anion sites, and the resultant carrier concentration reaches ≈3 × 1019 cm-3 or below. This is much lower than the optimum theoretically predicted, which suggets that further improvements will be possible once a highly efficient dopant is found. Yttrium, a trivalent dopant, is shown to enable carrier concentrations up to and above ≈1 × 1020 cm-3 when it is doped on the cation site. Such carrier concentration allows for in-depth understand of the electronic transport properties over a broad range of carrier concentrations, based on a single parabolic band approximation. As well as reasonably high carrier mobility in coarse-grain materials sintered by hot deforming and fusing of large pieces of ingots synthesized by melting, higher thermoelectric performance than earlier experimentally reported for n-type Mg3 Sb2 is found. In particular, the thermoelectric figure of merit, zT, is even higher than that of any known n-type thermoelectric, including Bi2 Te3 alloys, within 300-500 K. This might pave the way for Mg3 Sb2 alloys to become a realistic material for n-type thermoelectrics for sustainable applications.