Influence of growth rate and orientation on thermoelectric properties in Mg₃Sb₂ crystal

Ag-doped Mg₃Sb₂ single crystal was successfully grown via a directional solidification method with high temperature gradient. The influence of microstructure, growth rate, and orientation on the thermoelectric properties was investigated. It was revealed that the changed growth rate results in a slight adjustment of chemical composition in Mg₃Sb₂ crystal. The crystal exhibits better thermoelectric performance at the rate of 18 mm h⁻¹. The Seebeck coefficient (S) and electrical conductivity (σ) are anisotropic in [001] and [100] orientation. The thermal conductivity exhibits isotropic property. The top value of Seebeck coefficient is 267 µV K⁻¹ in the [001] orientation, which is dramatically improved compared with previous results. As a consequence, the maximum value of the power factor for the [001]-oriented crystal is 1.21 m Wm⁻¹K⁻² at v = 18 mm h⁻¹, which results in an elevated ZT of 0.68. This result is verified well by Hall testing and density functional theory calculations.