Low lattice thermal conductivity of novel NiVSn with 19 valence electron count contrasted to 18 of NiVAl and NiAlSb Half-Heusler compounds

Abstract

In the current study, the novel pristine compounds of both VEC 18 (NiVAl & NiAlSb) and VEC 19 (NiVSn) materials have been synthesized employing arc-melting and hot-pressed at 1073 K. The measured carrier concentration for all the compounds was found ∿ 1020-1021 cm−3. Further, NiAlSb, NiVAl, and NiVSn half-Heusler (HH) compounds exhibited n-type semiconductor behaviour, with maximum Seebeck coefficients (S) of −50.2 μV/K, −40.5 μV/K, and −14.5 μV/K at 723 K. As a result of the measured S and electrical conductivity, the estimated power factor for NiVSn (0.20 mWm−1K−2), NiAlSb (0.41 mWm−1K−2), and NiVAl (0.65 mWm−1K−2) at 723 K. The NiVSn lattice thermal conductivity (κl) was reduced to ∿ 79.80 % and 76.71 % as compared to NiAlSb and NiVAl compounds. Despite having reduced κl, low zT exhibited for NiVSn compound mainly due to nominal S. The reduced κl was mainly attributed to weak chemical bonding results from lower group velocity of phonon, leading to a higher anharmonicity effect in the lattice. Therefore, NiVSn of VEC 19-based compound can be considered as a potential candidate material for TE applications other than traditional 18-VEC HH compounds. The thermoelectric performance of the novel HH compounds is suitably corroborated with the structural and microstructural investigations.