Electronic structure of protonic conductor SrCeO3 by soft-X-ray spectroscopy

The electronic structure of protonic conductor SrCe1−xYxO3−δ (x=0, 0.05) has been studied by resonant-photoemission spectroscopy (RPES) and X-ray absorption spectroscopy (XAS) in the soft-X-ray region. The RPES spectra exhibit that the O 2p state strongly hybridizes with Ce 4f state in the valence band. The valence band consists of the mixed-valent states of the 4f0 (Ce4+) and 4f1L (Ce3+) configurations. The XAS spectra in the band gap energy region show a hole state at the top of the valence band and an acceptor-induced level just above the Fermi level (EF). The energy position of the hole state accords with that of the Ce3+ state. The energy separation between the hole state and EF is in good agreement with the activation energy.