Impact of strain-induced electronic topological transition on the thermoelectric properties of PtCoO$_2$ and PdCoO$_2$

TL;DR

This study uses first-principles calculations to show that epitaxial strain significantly alters the thermoelectric properties of PtCoO₂, especially its thermopower, due to changes in the electronic structure and Fermi surface topology.

Contribution

It reveals the strain-induced topological transition's impact on thermoelectric properties of PtCoO₂, highlighting high sensitivity of out-of-plane transport to strain.

Findings

Thermopower varies from -107 μV/K to -303 μV/K with strain.

Strain causes Fermi surface topology changes involving additional band crossings.

Predicted thermoelectric figure of merit ZT reaches 0.25 at 600 K for strained PtCoO₂.

Abstract

By a combination of first-principles calculations and semi-classical Boltzmann transport theory, we investigate the effect of epitaxial strain on the electronic structure and transport properties of PtCoO$_2$ and PdCoO$_2$. In contrast to the rather uniform elastic response of both systems, we predict for PtCoO$_2$ a high sensitivity of the out-of-plane transport properties to strain, which is not present in PdCoO$_2$. At ambient temperature, we identify a considerable absolute change in the thermopower from $-107\,\mu$V/K at $-5\,$\% compressive strain to $-303\,\mu$V/K at $+5\,$\% tensile strain. This remarkable response is related to distinct changes of the Fermi surface, which involve the crossing of two additional bands at a moderate compressive in-plane strain. Combining our transport results with available experimental data on electrical and lattice thermal conductivity we predict a thermoelectric figure of merit of up to $ZT$$\,=\,$$0.25$ at $T$$\,=\,$$600\,$K for strained PtCoO$_2$.