Enhancement of the thermoelectric performance of β-Zn4Sb3 by in situ nanostructures and minute Cd-doping

β-Zn4Sb3 compounds doped with minute amounts of Cd were synthesized by the MS-SPS technique, which involves melt spinning (MS) followed by spark plasma sintering (SPS), and the microstructures, thermoelectric and thermodynamic properties were systematically characterized. The non-equilibrium MS-SPS technique generates multi-scale nanostructures in the MS-prepared ribbon-shape samples and the resulting compacted bulk materials. These unique multiple nanostructures result in substantial reductions in lattice thermal conductivities, particularly for samples with a large number of ZnSb nanodots with sizes of 10–30 nm. Meanwhile, Cd-doping remarkably improves the electrical properties of the (Zn1−xCdx)4Sb3 compounds by a slight decrease in electrical conductivity and an apparent enhancement of the Seebeck coefficient. Therefore, the dimensionless figure of merits are significantly improved and the maximum value reaches ∼1.30 for the (Zn0.99Cd0.01)4Sb3 sample at 700 K, representing ∼13% and ∼23% improvements compared with the undoped MS-SPS sample and the 1% Cd-doped melting ingot, respectively. In particular, this value shows no degradation after 10 heat cycles from 300 to 700 K or 30 h annealing at 680 K in vacuum, whereas the ZT of neat sample decreases by ∼20% to a relatively low value of ∼1.0 after 30 h annealing. The enhanced thermal stability of ZT along with the suppressing effect on the low-temperature α–β phase transition clearly indicates a large improvement in thermodynamic stability as a result of minute Cd-doping. All the above-mentioned benefits make the minute Cd-doped β-Zn4Sb3 compound prepared by the MS-SPS technique a promising candidate for mid-range temperature thermoelectric power generation applications.