Electronic thermal conductivity as derived by density functional theory

Abstract

Reliable evaluation of the lattice thermal conductivity is of importance for optimizing the figure-of-merit of thermoelectric materials. Traditionally, when deriving the phonon mediated thermal conductivity ${\kappa }_{ph}=\kappa -{\kappa }_{el}$ from the measured total thermal conductivity $\kappa$ the constant Lorenz number $L_0$ of the Wiedemann-Franz law \mbox{${\kappa }_{\mathbf{el}}=T{L}_0\sigma$} is chosen. The present study demonstrates that this procedure is not reliable when the Seebeck coefficient $|S|$ becomes large which is exactly the case for a thermoelectric material of interest. Another approximation using $L_0-S^2$, which seem to work better for medium values of $S^2$ also fails when $S^2$ becomes large, as is the case when the system becomes semiconducting/insulating. For a reliable estimation of ${\kappa }_{el}$ it is proposed, that a full first-principles calculations by combining density functional theory with Boltzmann's transport theory has to be made. For the present study such an approach was chosen for investigating the clathrate type-I compound Ba${}_8$Au${}_{6-x}$Ge${}_{40+x}$ for a series of dopings or compositions $x$. For a doping of $0.8$ electrons corresponding to $x=0.27$ the calculated temperature dependent Seebeck coefficient agrees well with recent experiments corroborating the validity of the density functional theory approach.

5 pages, 5 figures

References in corpus (2)

• BoltzTraP. A code for calculating band-structure dependent quantities
• Low thermal conductivity of the layered oxide (Na,Ca)Co_2O_4: Another example of a phonon glass and an electron crystal

Cited by in corpus (2)

• High Thermoelectric Performance in Two-Dimensional Tellurium: An Ab Initio Study
• Methodology for determining the electronic thermal conductivity of metals via direct non-equilibrium ab initio molecular dynamics