Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 88: Electronic Structure Theory: New Concepts and Developments in Density Functional Theory and Beyond - VI
O 88.3: Vortrag
Donnerstag, 23. März 2017, 11:00–11:15, GER 38
Finite-temperature properties of the thermoelectric clathrate Ba8AlxSi46−x — •Maria Troppenz, Santiago Rigamonti, and Claudia Draxl — Humboldt-Universität zu Berlin
Intermetallic clathrate compounds are promising candidates for high-efficiency thermoelectric (TE) applications. Here, we study Ba8AlxSi46−x in the composition range x ∈ [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 Zintl 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 TE 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. 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 Zintl composition is close to the typical temperatures at which the figure of merit of TE clathrates is maximal. Signatures of the transition in the entropy, order parameter, specific heat, and canonical distribution are analyzed for the full composition range.
[1] J. H. Roudebush et al.; Inorg. Chem. 51, 4161 (2012)
[2] M. Troppenz, S. Rigamonti and C. Draxl; preprint.
[3] F. Wang and D. P. Landau, Phys. Rev. Lett. 86, 2050 (2001)