Half-Heusler Alloys for Efficient Thermoelectric Power Conversion

Abstract

Half-Heusler (HH) phases (space group F43m, Cl b ) are increasingly gaining attention as promising thermoelectric materials in view of their thermal stability and environmental benignity as well as efficient power output. Until recently, the verifiable dimensionless figure of merit (ZT) of HH phases has remained moderate near 1, which limits the power conversion efficiency of these materials. We report herein ZT~1.3 in n-type (Hf,Zr)NiSn alloys near 850 K developed through elemental substitution and simultaneously embedment of nanoparticles in the HH matrix, obtained by annealing the samples close to their melting temperatures. Introduction of mass fluctuation and scattering centers play a key role in the high ZT measured, as shown by the reduction of thermal conductivity and increase of thermopower. Based on computation, the power conversion efficiency of a n-p couple module based on the new n-type (Hf,Zr,Ti)NiSn particles-in-matrix composite and recently reported high-ZT p-type HH phases is expected to reach 13%, comparable to that of state-of-the-art materials, but with the mentioned additional materials and environmental attributes. Since the high efficiency is obtained without tuning the microstructure of the HalfHeusler phases, it leaves room for further optimization.

Enhanced Figure of Merit in Bismuth-Antimony Fine-Grained Alloys at Cryogenic Temperatures

“…The Lorenz numbers used in the calculation were obtained from the Seebeck coefficient based on the empirical equation proposed by H. S. Kim etc. 33 34 .…”

Odyssey of thermoelectric materials: foundation of the complex structure

“…Sb is found to be an effective dopant for n-type ZrNiSn half-Heusler alloys which effectively increases the carrier concentration and also reduces thermal conductivity [36]. Chen et al reported high zT of 1.3 in n-typeHf 0.65 Zr 0.25 Ti 0.15 NiSn 0.995 Sb 0.005 /nano-ZrO 2 composition at 850 K [195]. Such high zT resulted from Figure 15.…”

“…Due to Ti substitution, phonon scattering is enhanced which reduces lattice thermal conductivity. On the other hand, ZrO 2 nanoparticles act as potential barriers for carrier scattering that enhances the thermopower [195]. Among the prospective half-Heusler alloys are also p-type FeNbSb and α-MgAgSb based materials [196,197].…”

Multi-Principal-Element Approach to High-Performance Thermoelectric Materials

“…The results show that thermoelectric MPEA have high ZT comparable to that of state-of-the-art materials. The high-ZT MPEA (filled symbols) shown in Figure 4 include: Bi0.5Sb1.5Te2.7Se0.3, 1.12, 303 (Xu et al, 2012), where the first number is ZT and second number is the temperature at which ZTmax occurs; (GeTe)80(AgSbTe2)20, 1.75, 773 ; (PbTe)0.84(PbSe)0.07(PbS)0.07Na0.02, 2, 800 (Korkosz et al, 2014); Pb0.92Mg0.08Te0.8Se0.2Na0.02, 2.2, 820 (Fu, 2016); Cu0.8Ag0.2In0.5Ga0.5Te2, 1.6, 900 ; Cu1.95Ag0.05S1/3Se1/3Te1/3, 1.9, 1000 ; Ti0.5Zr0.25Hf0.25NiSn, 1.5 820 (Rogl et al, 2018); Hf0.65Zr0.25Ti0.15NiSn0.995Sb0.005, 1.3, 830 (Chen et al, 2016); ZrCoBi0.65Sb0.15Sn0.20, 1.4 970 ; Ta0.74V0.1Ti0.16FeSb. 1.52, 973 (Zhu et al, 2019).…”

“…Each symbol may represent several alloys with the same ZT. Mass and strain fluctuations from Hf/Zr/Ti and nanostructure enhance phonon scattering (Chen, 2016) Ti0.5Zr0.25Hf0.25NiSn0.98Sb0.02 n-type 1.2 Phase separation and mass and strain fluctuations (Gürth, 2016) Ti0.5Zr0.25Hf0.25NiSn n-type 1.5 Phase separation and mass and strain fluctuations (Rogl, 2018) FeNb0.86Hf0.14Sb single dopant p-type 1.5…”