Dresden 2017 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 22: Poster session I

MM 22.36: Poster

Monday, March 20, 2017, 19:00–20:00, P4

Understanding chemical ordering in intermetallic clathrates — •Mattias Ångqvist and Paul Erhart — Department of Physics, Chalmers University of Technology, Sweden

Clathrates are periodic structures that provide a framework that can trap large, loosely bound species. Intermetallic clathrates often have low thermal lattice conductivity and high electric conductivity, which makes them interesting candidates for thermoelectric applications. These materials exhibit a great variability with respect to elemental composition and the distribution of the species, which provides flexibility for tuning properties but also poses a challenge with regard to developing a comprehensive understanding of these systems. Here, we demonstrate a method that can both accurately and efficiently sample this compositional space. We use density functional theory calculations to parametrize alloy cluster expansions (CE) to obtain ab-initio accuracy in Monte Carlo simulations that can exhaustively sample the compositional space. We apply this methodology to study the chemical ordering and related effects in the binary clathrates Ba₈Al_xSi_46−x, Ba₈Al_xGe_46−x, Ba₈Ga_xGe_46−x, and Ba₈Ga_xSi_46−x in terms of composition and temperature. We validate our method by predicting the site occupancy factors (SOFs) and achieve excellent agreement with experimental results. This validation enables us to provide a rationale for the extreme SOF behavior with varying Al content by looking at the actual interactions found in the CE. Finally, we address the contributions of chemical ordering on heat capacity and lattice expansion.