Mapping Thermoelectric Transport in a Multicomponent Alloy Space

TL;DR

This paper develops analytic models to predict how alloy composition affects thermoelectric transport, revealing that adding intermediate-mass elements can increase thermal conductivity unless multiple independent scattering mechanisms are introduced.

Contribution

It introduces a multicomponent extension of alloy scattering models and applies thermodynamic functions to generalize transport predictions across complex alloy systems.

Findings

Maximal lattice thermal conductivity occurs along binary alloys with highest mass contrast.

Adding intermediate-mass atoms can increase thermal conductivity unless multiple scattering mechanisms are present.

The models successfully predict transport behavior across various pseudo-ternary and pseudo-quaternary alloys.

Abstract

Interest in high entropy alloy thermoelectric materials is predicated on achieving ultralow lattice thermal conductivity $\kappa\sub{L}$ through large compositional disorder. However, here we show that for a given mechanism, such as mass contrast phonon scattering, $\kappa\sub{L}$ will be minimized along the binary alloy with the highest mass contrast, such that adding an intermediate-mass atom to increase atomic disorder can increase thermal conductivity. Only when each component adds an independent scattering mechanism (such as adding strain fluctuation to an existing mass fluctuation) is there a benefit. In addition, both charge carriers and heat-carrying phonons are known to experience scattering due to alloying effects, leading to a trade-off in thermoelectric performance. We apply analytic transport models, based on perturbation and effective medium theories, to predict how alloy scattering will affect the thermal and electronic transport across the full compositional range of several pseudo-ternary and pseudo-quaternary alloy systems. To do so, we demonstrate a multicomponent extension to both thermal and electronic binary alloy scattering models based on the virtual crystal approximation. Finally, we show that common functional forms used in computational thermodynamics can be applied to this problem to further generalize the scattering behavior that is modeled.