Microstructure and thermoelectric properties of un-doped Mg 2 Si 1−x Sn x single crystals prepared by high temperature gradient directional solidification

Un-doped single crystals of Mg2Si1−xSnx (x = 0.55, 0.65 and 0.75) were successfully prepared by high temperature gradient directional solidification (HGDS). In the Mg2Si0.45Sn0.55 crystal, Mg2Si precipitates were observed in the solidified microstructure, and no precipitates in the single crystals of Mg2Si0.35Sn0.65 and Mg2Si0.25Sn0.75. By measuring the electronic transport properties of these three single crystals, the Mg2Si0.35Sn0.65 has a largest PF value, about 2.5 times more than that of the nanocrystalline prepared by solid-state reaction methods. The corresponding ZT values of Mg2Si0.35Sn0.65 single crystal are greatly improved. It indicates that, the Mg2Si1−xSnx crystals prepared by HGDS can not only have a uniform microstructure, but also optimize the TE performance of the crystal. In addition, the first-principles calculation has been conducted to examine the intrinsic properties of Mg2Si1−xSnx single crystals, and the calculated data agree well with the experimental results.