Beyond the constant Lorenz number for separating thermal con - ductivities of electrons and phonons : A DFT study 1

Submitted for the MAR13 Meeting of The American Physical Society Beyond the constant Lorenz number for separating thermal conductivities of electrons and phonons: A DFT study1 MINGXING CHEN, Department of Physics, University of Wisconsin-Milwaukee, RAIMUND PODLOUCKY, Department of Physical Chemistry, University of Vienna, Austria — Lorenz number is an important quantity for separating thermal conductivities of electrons and phonons in the field of thermoelectrics, which is materialand temperature-dependent. Combing DFT calculations with Boltzmann transport equations, we have derived the Lorenz number for realistic compound BaAu6Ge40, a good thermoelectric material. It is demonstrated that using the constant Lorenz number of the Wiedemann-Franz law for simple metals leads to strong discrepancies, in particular at higher temperatures. The results suggest that one has to rethink the way of extracting both κel and κph as usually done based on the measured electrical conductivity. We propose a strategy of correcting the Wiedemann-Franz Lorenz number that subtracts the metallic limiting value by S2 as obtained from Seebeck measurements. 1The authors gratefully acknowledge the support by the Austrian Science Foundation FWF under project nr. P22295-N20. Mingxing Chen Department of Physics, University of Wisconsin-Milwaukee Date submitted: 09 Nov 2012 Electronic form version 1.4