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

beta-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)(4)Sb-3 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 similar to 1.30 for the (Zn0.99Cd0.01)(4)Sb-3 sample at 700 K, representing similar to 13% and similar to 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 similar to 20% to a relatively low value of similar to 1.0 after 30 h annealing. The enhanced thermal stability of ZT along with the suppressing effect on the low-temperature alpha-beta 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 beta-Zn4Sb3 compound prepared by the MS-SPS technique a promising candidate for mid-range temperature thermoelectric power generation applications. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.