Berlin 2015 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 24: Thermoelectricity

HL 24.2: Talk

Tuesday, March 17, 2015, 09:45–10:00, EW 202

Density functional calculations of the thermoelectric properties of ZrNiSn and ZrCoBi — •Gregor Fiedler and Peter Kratzer — Faculty of Physics, University Duisburg-Essen, 47048 Duisburg, Germany

Finding "green", inexpensive and efficient materials combinations for thermoelectric energy harvesting is a challenge. We have conducted a theoretical study of ZrCoBi, ZrNiSn and their heterostructures for thermoelectric applications. We present results from first-principles calculations for all factors contributing to the figure of merit ZT. Using density functional theory, we compute the electronic and phononic spectrum, deformation potentials and elastic constants. From the electronic band structure, the Seebeck coefficient and the electronic conductivity are calculated. For the latter, acoustic intravalley scattering is included using the calculated deformation potentials. Moreover, we show that disordered and off-stoichiometric materials display defects states in the band gap. The unavoidable occurrence of these defects due to their low formation energy is responsible for the very small band gap in ZrNiSn reported experimentally, and the high thermal carrier concentration. In heterostructures of ZrNiSn and ZrCoBi, the thermal conductivity is predicted to be substantially reduced. We estimate this reduction using the diffuse mismatch model based on the calculated phonon spectra, including optical phonons.