The electronic states of Ba8Ga16Ge30 and Sr8Ga16Ge30 are studied by soft x-ray photoelectron spectroscopy (XPS) at a high-energy facility. In Ba 8Ga16Ge30, three bands are resolved in the valence band region. Resonance experiments together with theoretical calculations show that the three band structures in the valence band are mainly constructed by the Ge/Ga 4s and 4p wave functions with little contributions of Ba 5s, 5p and 5d. The valence band of Sr8Ga16Ge 30 shows a similar feature to that of Ba8Ga 16Ge30. It is clearly shown that the atomic orbitals of Ba and Sr make little hybridization with the orbitals made by the framework polyhedra. This provides the understanding of the thermoelectricity in clathrates, and assists the design in high performance thermoelectric materials in this family.
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