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Suppression of thermal conductivity without impeding electron mobility in n-type XNiSn half-Heusler thermoelectrics

DOI: 10.1039/C9TA10128D DOI Help

Authors: S. A. Barczak (Heriot-Watt University) , R. J. Quinn (Heriot-Watt University) , J. E. Halpin (University of Glasgow,) , K. Domosud (Royal Holloway University London) , R. I. Smith (ISIS Facility) , A. R. Baker (Diamond Light Source) , E. Don (SemiMetrics Ltd) , I. Forbes (Northumbria University) , K. Refson (Royal Holloway University London) , D. A. Maclaren (University of Glasgow) , J. W. G. Bos (Heriot-Watt University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Materials Chemistry A , VOL 26

State: Published (Approved)
Published: November 2019
Diamond Proposal Number(s): 14032

Open Access Open Access

Abstract: We outline a strategy to improve the thermoelectric performance of n-type XNiSn based half-Heusler alloys through Cu doping into vacant tetrahedral sites. A comprehensive combination of structural characterisation and modelling is employed to discriminate the competing mechanisms for thermoelectric enhancement. During synthesis a mineralising effect occurs that improves the homogeneity of the alloying elements Ti, Zr and Hf, and promotes grain growth, leading to a doubling of the electron mobility. In the formed materials, Cu is a strong n-type dopant, like Sb, but occupies the interstitial site and strongly enhances phonon scattering without diminishing carrier mobility (in contrast to interstitial Ni). Simultaneous alloying with Ti, Zr and Hf serves to minimise the thermal conductivity via regular mass disorder and strain effects. A best electronic power factor, S2/ρ, of 3.6 mW m−1 K−2 and maximum ZT of 0.8 at 773 K were observed for a Ti0.5Zr0.25Hf0.25NiCu0.025Sn composition, enabling promising device power densities of ∼6 W cm−2 and ∼8% conversion efficiency from a 450 K gradient. These findings are important because they provide new insight into the mechanisms underpinning high ZT in the XNiSn system and indicate a direction for further improvements in thermoelectric performance.

Diamond Keywords: Thermoelectric Generators; Alloys

Subject Areas: Chemistry, Materials, Energy

Instruments: I11-High Resolution Powder Diffraction

Added On: 27/11/2019 15:05


Discipline Tags:

Physical Chemistry Earth Sciences & Environment Climate Change Energy Sustainable Energy Systems Materials Science Metallurgy Quantum Materials Thermoelectrics Chemistry

Technical Tags:

Diffraction X-ray Powder Diffraction