Dresden 2017 – scientific programme

Parts | Days | Selection | Search | Updates | Downloads | Help

HL: Fachverband Halbleiterphysik

HL 71: Transport Properties

HL 71.3: Talk

Thursday, March 23, 2017, 10:00–10:15, POT 112

Thermal conductivity in intermetallic clathrates: A first-principles perspective on the phonon-glass concept — •Daniel Lindroth, Mattias Ångqvist, and Paul Erhart — Chalmers University of Technology, Department of Physics, Gothenburg, Sweden

Clathrates exhibit a very low thermal conductivity, which is a key factor for their very good thermoelectric properties and has been attributed to "phonon-glass" conduction behavior. Here, we present a computational analysis of the conduction mechanism using Ba8X16Y30 (X={Al,Ga}, Y={Si,Ge}) as model systems. Contributions to the thermal conductivity from both electrons as well as phonons are computed with Boltzmann transport theory.

The calculations are in good agreement with experimental data and in particular reproduce the experimentally observed ordering of the lattice thermal conductivity between the different systems. We demonstrate that these rather non-intuitive trends can be traced to the presence (or lack thereof) of dispersed higher frequency optical phonon modes, which provide a surprisingly large contribution to the lattice thermal conductivity. The "phonon-glass" behavior manifests itself in our calculations in the form of very short lifetimes, which indicate that already at room temperature the majority of modes is overdamped.

In terms of the electronic thermal conductivity, our results provide insight into the applicability of the Wiedemann-Franz law. While the latter is regularly used to separate lattice and electronic contributions to the thermal conductivity, our data show that the choice of pre-factor can incur an error of up to 50% for the electronic thermal conductivity.