Structural and electronic properties of tin clathrate materials - art. no.165202

Using an ab initio local density approximation (LDA) method, we have studie d the structural properties and the electronic band structures of several t in-based clathrate materials. We find that the pure type-I (Sn-46) and type -II (Sn-136) clathrate frameworks are metastable, expanded-volume phases of Sn and that they are semiconductors. We further find that the Cs encapsula ted type-I binary clathrate is metallic if full stoichiometry (Cs8Sn46) is assumed. However, our calculations suggest that vacancy formation is energe tically favored, and that the stable vacancy compound Cs(8)Sn(44)square (2) is a narrow gap semiconductor. We have also studied the ternary clathrate compounds Cs8Ga8Sn38 and Cs8Zn4Sn42, which have been suggested as potential thermoelectrics, and we find that these are semiconductors. The trends in the structural and electronic properties of these Sn-based clathrates are d iscussed, and our results are compared with experiment where possible.