Open-structured materials: Skutterudites and clathrates

There are a large number of inorganic compounds with open-framework structures that entrap atoms or molecules within the lattice. Of these, the skutterudites and type I clathrates have gained the greatest attention from the perspective of thermoelectric applications. The crystal structure of these materials can be considered as being open in the sense that they possess voids whereby interstitially placed atoms are bounded loosely, thereby creating localized disorder in an otherwise well-ordered, covalently bonded lattice. The optimum situation occurs if the intrinsic mobility is relatively high due to the well-ordered, periodic structure of the crystal framework while the phonons are scattered by localized disorder. Substantial experimental and theoretical research has been devoted to these two material systems over the past decade. This effort has shown that the physical properties are directly related to their unique crystal structures, as well as the different compositions that can be synthesized in order to modify these physical properties.