Optimized electronic performance in half-Heusler Ti-doped NbFeSb materials by stoichiometric tuning at the Fe and Sb sites

Abstract

Electronic structure is known to be highly influenced by the site occupancy and the stoichiometry of the material which in turn largely effects the thermoelectric properties. Herein, we present electronic calculations using density functional theory (DFT) of non-stoichiometric Ti doped NbFeSb configuration, showing the effect of the anti-site Fe atoms on the electronic properties, and supporting them with experimental results of the prepared Nb0.8Ti0.2Fe1+xSb1−x samples. The electronic structure of the non-stoichiometric sample shows the introduction of two distinct peaks near the Fermi level by the Fe atoms at the Sb sites. These resonance states are known to cause an increase in the density of states effective mass near the Fermi level, which explains the increase in the Seebeck coefficient in the sample x = 0.03 compared to the sample x = 0.00. In addition, a comparatively higher electrical conductivity is reported from sample x = 0.03, which is attributed to the aliovalent substitution of Sb atoms by Fe atoms. The simultaneous increase in the Seebeck coefficient and electrical conductivity culminates in an increased power factor of ∼50.3 µW/cmK2 at 373 K, which is ∼46% higher than that of samples x = 0.00 and x = 0.05, highlighting the possibility of increasing the power density by stoichiometric variation to achieve the high joule-per-dollar performance of NbFeSb-based TE devices, the relevance of which is also currently emphasized in the quest for commercial viability.