2017/01/26 by Maria Troppenz, Santiago Rigamonti, Claudia Draxl
Chemistry · Engineering · Materials Science · Physics and Astronomy · #Advanced Thermoelectric Materials and Devices #Atomic physics #Chemistry #Condensed matter physics #Electronic structure #Ground state #Heusler alloys: electronic and magnetic properties #Intermetallics and Advanced Alloy Properties #Materials science #Physical chemistry #Physics #Thermodynamics #Thermoelectric effect #cond-mat.mtrl-sci
paper · pdf · doi:10.1021/acs.chemmater.6b05027
published as Chem.Mater. 29 (2017) 2414-2424 · 9 figures
openalex publication_date 2017/01/26 · openalex created_date 2017/02/03 · arxiv created 2017/08/27 · arxiv updated 2017/08/29 · openalex updated_date 2026/08/05
The structural and electronic properties of the clathrate compounds Ba 8 Al x Si 46– x and Sr 8 Al x Si 46– x are studied from first-principles, considering an Al content x between 6 and 16. Due to the large number of possible substitutional configurations, we make use of a special iterative cluster-expansion approach, to predict ground states and quasi-degenerate structures in a highly efficient way. These are found from a simulated annealing technique where millions of configurations are sampled. For both compounds, we find a linear increase of the lattice constant with the number of Al substituents, confirming experimental observations for Ba 8 Al x Si 46– x . Also the calculated bond distances between high-symmetry sites agree well with experiment for the full compositional range. For x being below 16, all configurations are metallic for both materials. At the charge-balanced composition ( x = 16), the substitutional ordering leads to a metal–semiconductor transition, and the ground states of Ba 8 Al 16 Si 30 and Sr 8 Al 16 Si 30 exhibit indirect Kohn–Sham band gaps of 0.36 and 0.30 eV, respectively, while configurations higher in energy are metals. The finding of semiconducting behavior is a promising result in view of exploiting these materials in thermoelectric applications.