Anisotropic electronic transport properties of Ag-oped Mg3Sb2 crystal prepared by directional solidification

Ag-doped Mg3Sb2 crystals are successfully grown via a directional solidification method with high temperature gradient. The microstructure of the crystal is homogeneous and without precipitation. Both electrical conductivity and Seebeck coefficient are anisotropic in two crystallographic directions ([001] and [101]) due to anisotropic effective mass and mobility of the carriers. Thermal conductivity is isotropic too, and the maximum Seebeck coefficient is 265 μV K−1 in the [001] orientation, which represents a substantial improvement over previous results. As a consequence, the maximum power factor for the 2.5 at. % Ag-doped crystal is 1.21 mW m−1 K−2 in the [001] orientation, which results in an elevated ZT of 0.67 at T = 800 K. First principles calculations and Hall measurements are used to verify the experimental results.