Enhanced thermoelectric properties of Hf-free half-Heusler compounds prepared via highly fast process

Hf-free n-type half-Heusler with a nominal composition of Ti0.5Zr0.5NiSn0.98Sb0.02 has been reported to have a high ZT value of almost 1.2. However, the synthesis process requires a long annealing time to achieve single-phase structure, which contributes to high product costs due to energy and time consumption. Here we introduce a new route to prepare (Ti0.5Zr0.5)(1-x)NbxNiSn (x = 0, 0.0050, 0.0075, 0.0100, 0.0125, 0.0150, 0.0175 and 0.0200) compounds for high thermoelectric (TE) performance along with shortening time for sample preparation. The samples were prepared by a combination of arc-melting (AM) and melt-spinning (MS) followed by spark plasma sintering process (SPS). The combination of these synthetic methods produced (Ti0.5Zr0.5)(1-x)NbxNiSn samples with high chemical homogeneity, single-phase structure, and fine grain about 300 nm in size, which are preferred for both charge and phonon transport properties. As a result, a maximum power factor of 44.5 mu W cm(-1) K-2 at 817 K and a maximum ZT of 1.19 at 874 K were achieved for the sample with x = 0.015, which are comparable to the highest ZT value reported so far for the Hf-free n-type MNiSn (M = Ti, Zr) compounds. The calculated output power density P-d and efficiency eta based on a single-leg device showed an excellent performance, which yields the maximum P-d of 16.2 W cm(-2) and eta of 12.08% at the cold side temperature T-c approximate to 305 K and the hot side temperature T-H approximate to 875 K for the optimized composition with x = 0.0125. Furthermore, it is noted that the synthetic process here does not require a long-annealing time and it can be easily applied to mass production. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

A new synthetic method was introduced to prepare high-performance (Ti0.5Zr0.5)(1-x)NbxNiSn compounds, achieving high chemical homogeneity, single-phase structure, and fine grain size of about 300 nm. The maximum ZT value of 1.19 was achieved, comparable to the highest reported for similar compounds, with promising output power density and efficiency.