Synergistic defect engineering for improving n-type NbFeSb thermoelectric performance through high-throughput computations†
Abstract
The p-type NbFeSb half-Heusler compound has been proved to be a promising high-temperature thermoelectric material, and many works have been devoted to improving its properties. However, its corresponding n-type compound shows a fairly low ZT, which greatly hampers its realistic applications due to the asymmetrical performance in thermoelectric devices. In this work, we compute in a high-throughput manner a large amount of (intrinsic and extrinsic) defects in NbFeSb, and systematically investigate their effects on the n-type thermoelectric performance (electrical and thermal properties). For electrical properties, the intrinsic defects of FeNb antisites and Fei interstitials have low formation energies, and their donor behavior is favorable for n-type conductivity. The extrinsic defects (such as CoNb and Pti), on the other hand, introducing strong resonant states slightly above the conduction band maximum, can greatly enhance the power factor (PF) of n-type: noticeably 2–3 times higher than that of the intrinsic NbFeSb compound. For thermal properties, the low-energy extrinsic defects of F/Cl/P/S substitution at Sb sites can significantly reduce the lattice thermal conductivity (lowered to 1.25 W m−1 K−1 at 300 K) due to the large-disorder scatterings. Unfortunately, none of the defects simultaneously satisfy the three criteria for promising n-type NbFeSb thermoelectrics (having low formation energy, showing strong resonant states and depressing the lattice thermal conductivity). Therefore, we propose a synergistic defect strategy for those low-energy defects: some (CoNb or Pti) boosting the PF and others (FSb, ClSb, SSb or PSb) suppressing the thermal conductivity. Our work benefits future experimental defect engineering of NbFeSb-based materials and paves the way to narrow the gap between the n- and p-type thermoelectric properties.
- This article is part of the themed collection: Journal of Materials Chemistry A HOT Papers