In situ synthesis and thermoelectric properties of La-doped Mg ₂(Si, Sn) composites

Utilizing the peritectic reaction and the miscibility gap featured in the pseudo-binary phase diagram of Mg₂Si and Mg₂Sn, we fabricated environmentally friendly Mg₂(Si, Sn) thermoelectric (TE) composites in which the Mg₂Si-rich bulk grains were in situ coated by Mg₂Sn-rich thin layers. The Mg₂Sn-rich grain boundary phase was selectively doped with La. It was found that the La doping dramatically increased the electrical conductivity to thermal conductivity ratio in the composites. As a result, a dimensionless figure of merit ZT ∼ 0.81 has been attained at 810 K for the Mg_2-xLa_x(Si, Sn) in situ composite with x = 0.005, significantly higher than the ZT ∼0.18 at 540 K for the undoped composite and comparable to ZT ∼ 0.8 of state-of-the-art PbTe intermediate temperature TE alloys.