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CAMP Seminar: Finite-temperature Properties of the Thermoelectric Clathrate Ba8AlxSi46-x

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Maria Troppenz, Institut für Physik and IRIS Adlershof, Humboldt-Universität zu Berlin
When
22 August 2017 from 4:00 PM to 4:30 PM
Where
339 Davey Laboratory
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Intermetallic clathrate compounds are promising candidates for high-efficiency thermoelectric applications. Here, we study Ba8AlxSi46-x in the composition range x ϵ [6,16] [1]. Recent theoretical studies [2] show a strong dependence of the electronic properties on configuration, i.e. the atomic arrangement of the substitutional Al atoms in the crystal framework. At the charge-balanced composition (x=16), the ground-state configuration is semiconducting. However, configurations higher in energy are metallic. Understanding this metal-semiconductor transition is essential, as semiconducting behavior is a prerequisite for thermoelectric applications. In this work, we employ the cluster expansion technique combined with Monte-Carlo simulations and the Wang-Landau method [3] to access finite-temperature properties, e.g. the temperature dependence of the band gap. We find that the transition is driven by a partial order-disorder transition of the substituents. Most importantly, it is found that the transition temperature (≈ 800 K) at the charge-balanced composition is close to the typical temperatures at which the figure of merit of thermoelectric clathrates is maximized. Signatures of the transition in the entropy, order parameter, specific heat, and canonical distribution are analyzed.

 

[1] J. H. Roudebush et al., Inorg. Chem. 51 4161 (2012).

[2] M. Troppenz, S. Rigamonti and C. Draxl, Chem. Mater. 29 2414 (2017).

[3] F. Wang and D. P. Landau, Phys. Rev. Lett. 86 2050 (2001).

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