Carrier scattering considerations and thermoelectric power factors of half-Heuslers

TL;DR

This study computationally examines the thermoelectric transport properties of half-Heusler alloys, emphasizing the dominant role of Coulombic scattering (POP and IIS) in determining power factors and providing insights for material design.

Contribution

It highlights the significant influence of Coulombic scattering processes on thermoelectric performance and offers a computationally efficient approach for estimating power factors.

Findings

Average peak TE power factors range between 5 and 10 mW/mK^2.

Ionized impurity scattering combined with polar optical phonons accounts for about 65% of the power factor determination.

Cheaper POP and IIS calculations provide acceptable first-order estimates of thermoelectric properties.

Abstract

The electronic and thermoelectric (TE) transport properties of 13 n-type and p-type half-Heusler alloys are computationally examined using Boltzmann transport. The electronic scattering times resulting from all relevant phonon interactions and ionized impurity scattering (IIS) are fully accounted for using ab initio extracted parameters. We find that at room temperature the average peak TE power factors (PF) of all materials we examine reside between 5 and 10 mW/mK$^2$. We also find that IIS in combination with the long range polar optical phonon (POP) scattering are more influential in determining the electronic transport and PF over all other non-polar phonon interactions (acoustic and optical phonon transport). In fact, the combination of POP and IIS determines the thermoelectric power factor of the half-Heuslers examined on average by about 65\%. The results highlight the crucial impact of Coulombic scattering process (POP and IIS) on the TE properties of half-Heusler alloys and provide profound insight for understanding transport, which can be applied widely in other complex bandstructure materials. In terms of computation expense, the computationally cheaper POP and IIS provide an acceptable first-order estimate of the power factor of these materials, while the non-polar contributions, which require more expensive ab initio calculations, could be of secondary importance.