Realizing p-type Mg₂Sn Thermoelectrics via Ga-Doping and Point Defect Engineering

Mg2Sn is a promising middle-temperature thermoelectric material consisting of earth-abundant, low-cost, and nontoxic elements. To obtain p-type Mg2Sn, a series of Mg2Sn1–xGax (x = 0, 0.005, 0.01, 0.02, and 0.03) ingots were synthesized by melting them under an Ar atmosphere. It was found that the ingots with x ≤ 0.02 were single crystals with Mg vacancies (VMg) as point defects. Ga doping increased chemical pressure, leading to an increase in the VMg fraction, and it also introduced hole carriers in Mg2Sn, which changed its conduction type from n-type to p-type. A maximum zT value of 0.18 at 450 K was obtained for p-type Mg2Sn0.98Ga0.02 single crystals, which had a lower total thermal conductivity than some other p-type Mg2Sn-based polycrystals.