Regensburg 2016 – scientific programme
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O: Fachverband Oberflächenphysik
O 88: Frontiers of Electronic Structure Theory: Focus on Topology and Transport V
O 88.7: Talk
Thursday, March 10, 2016, 16:30–16:45, H24
Structural and electronic properties of the thermoelectric clathrates Ba8AlxSi46−x and Sr8AlxSi46−x — •Maria Troppenz, Santiago Rigamonti, and Claudia Draxl — Humboldt-Universität zu Berlin
Clathrate compounds are promising candidates for high-efficiency thermoelectric applications.
Their cage-like structure containing guest atoms allows for exploiting the idea of
the phonon-glass electron-crystal and reaching a large figure of merit.
We study Ba8AlxSi46−x and
Sr8AlxSi46−x (6 ≤ x ≤ 16 ), where optimal electronic properties are expected close
to the Zintl composition (x = 16).
Cluster expansions on various quantities are performed, thus having access to ground-state as well as finite-temperature properties. A linear increase of the lattice constant with the number of Al substituents is obtained (0.019 Å per Al addition) confirming experimental observations (0.02 Å).
The calculated bond distances between high-symmetry sites agree well with experiment for the full compositional range [1,2]. We find a close correlation between bond distances and fractional Al occupancies. This helps improving models
used by experimentalists to estimate fractional occupancies.
The substitutional configurations present
an order-disorder transition
around 600−900 K, which is further analyzed applying the
Wang-Landau method.
An important finding is the semiconducting behavior of the low-temperature ordered phase at the Zintl composition, which points out the technological relevance of these compounds.
[1] J. H. Roudebush et al.; Inorg. Chem. 51, 4161 (2012)
[2] M. Bobnar et al.; Dalton Trans. 44, 12680 (2015)