XPS Study and First-Principles Calculations of the Structural and Electronic Properties of Type-VIII Clathrates Ba8Ga16-xCuxSn30

In the present work we report on the Single-crystal samples synthesis of type-VIII clathrates Ba8Ga16−xCuxSn30 (x = 0, 0.75, 1, 1.5, 2) by the Sn-flux method and the effects of Cu doping Ba8Ga16Sn30 have been investigated using x-ray photoemission spectroscopy (XPS). The structural and electronic properties have been studied by first-principles method based on the density-functional theory. We found that the Cu doping induced rearrangement of host-cage configuration, and consequently change of the electron transport properties. It was found that the binding energies for the Ba8Ga16−xCuxSn30 series decrease with increasing Cu substitution, resulting in a decrease of stability. Calculations indicate that these alloys are all indirect gap semiconductors and the band gap increases with increasing Cu content. Theoretical results indicate that Cu doping Ba8Ga16−xCuxSn30 should be p-type semiconductors, which does not agree with the previous experimental results.