Prediction of semiconducting clathrate materials: a promising finding for thermoelectricity

 

Figure 1: Clathrates form a complex caged structure (bottom left). The cages can accommodate "guest" atoms acting like rattlers (yellow spheres), efficiently lowering the thermal conductivity. This is highly beneficial for thermoelectrics. The electronic properties can be tailored by replacing some of the Si atoms which form the cages by x Al atoms. An extensive search for stable arrangements of Al atoms is performed (middle panel) and the lowest energy structures are found. For the charge-compensated composition (x=16) it is found that the most stable arrangement is semiconducting, while high-lying configurations are metallic (right panel).

Maria Troppenz, Santiago Rigamonti and Claudia Draxl have studied
the stability and electronic properties of clathrate compounds
Ba8AlxSi46–x and Sr8AlxSi46–x over a wide range of Al content,
employing a novel cluster-expansion technique.

Their finding of semiconducting behavior for the charge-compensated composition
is an exciting result in view of the possibility of exploiting these
materials in thermoelectric applications. Links to the paper and the
corresponding data in the NOMAD Repository are available at:

http://sol.physik.hu-berlin.de/index.php?page=publications