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Thermoelectric Property Study of Nanostructured p-Type Half-Heuslers (Hf, Zr, Ti)CoSb0.8Sn0.2



Based on the best peak theromoelectric figure-of-merit value (ZT) of ca. 0.8 in Hf0.5Zr0.5CoSb0.8Sn0.2 and ca. 1 in Hf0.8Ti0.2CoSb0.8Sn0.2, the effect of Ti on thermoelectric properties is studied in (Hf, Zr, Ti)CoSb0.8Sn0.2, with the aim of further improving the ZT and reducing the usage of Hf. By either partial replacement of Hf and Zr with Ti in Hf0.5Zr0.5CoSb0.8Sn0.2 or partial replacement of Hf and Ti with Zr in Hf0.8Ti0.2CoSb0.8Sn0.2, a peak ZT of ≥1 is achieved at 800°C in Hf0.44Zr0.44Ti0.12CoSb0.8Sn0.2. This composition has two advantages over the previous two best compositions: higher ZT than Hf0.5Zr0.5CoSb0.8Sn0.2 and less Hf than in Hf0.8Ti0.2CoSb0.8Sn0.2. A higher ZT with less Hf is very much desired since Hf is much more expensive than other constituent elements. The ZT improvement is the result of thermal conductivity reduction due to phonon scattering by both alloy and the nanostructure effect.