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DS: Fachverband Dünne Schichten

DS 50: Frontiers of Electronic Structure Theory: Focus on Topology and Transport V
(Joint session of DS and O, organized by O)

DS 50.7: Vortrag

Donnerstag, 10. März 2016, 16:30–16:45, H24

Structural and electronic properties of the thermoelectric clathrates Ba₈Al_xSi_46−x and Sr₈Al_xSi_46−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 Ba₈Al_xSi_46−x and Sr₈Al_xSi_46−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)