The structural and electronic properties of type-I clathrates Ba8CuxGa16-xSn30 from first-principle calculations

The effects of Cu-doping concentration on the structural and electronic properties of Ba8Cu (x) Ga16-x Sn-30 (0 a parts per thousand currency sign x a parts per thousand currency sign 3) type-I clathrate compounds have been investigated by first-principle calculations. Starting with the stable structures of the type-I clathrate semiconductors Ba8Ga16Sn30 containing no Ga-Ga bonds, we have constructed unit cells of Ba8Cu (x) Ga16-x Sn-30. The dependence of the structural and electronic properties of these compounds with x is discussed. The results reveal that the interaction between the rattler atom and the cage is affected by Cu doping, which suggests that Cu doping may play a role on the thermal conductivity. It is shown that the Ba8Ga16Sn30 is an intrinsic semiconductor, but Cu doping leads to p-type transport characteristics. Detailed analysis of the electronic structures for Cu-doped clathrates imply that Cu 3d electrons may display both itinerant and localized features and the electronic states near the top of the valence band are modified by the Cu 3d states. The number of states near the Fermi level is increased by the coupling of sp-d, which may lead to reduced stability of the structure.