Effect of single metal doping on the thermoelectric properties of SnTe

SnTe, a lead-free chalcogenide-based material, shows potential to achieve high thermoelectric performance. This report presents a comparative study of different metallic dopants in SnTe and their effect on its microstructures, and mechanical and thermoelectric properties. Doped SnTe (Sn1−xAxTe, A = Co, Ni, Zn, Ge, and x = 0.01, 0.03, 0.05) materials are prepared by melting–quenching synthesis followed by spark plasma sintering. X-ray powder diffraction analysis showed that the solubility of Co, Ni, and Zn in the structure is in the range from 0 to 0.01; however, Ge can be doped in higher amounts. The back-scattered electron images and elemental maps revealed that the CoTe, Ni3SnTe2 and ZnTe impurity phases precipitate on the grain boundaries in the SnTe matrix. Ge-doped samples have more uniform microstructures with a very few Ge-rich regions, which implies higher Ge solubility in agreement with the XRD results. The existence of impurity phases in the Co-, Ni-, and Zn-doped samples yields lower lattice thermal conductivities without deterioration in charge transport properties, leading to higher ZT values relative to the pristine SnTe sample. The microhardness of the doped samples is also improved due to the crack growth suppression and crack branching.