Electronic structure of proton conducting BaCe0.90Y0.10O3−δ

The electronic structure of the protonic conductor Y-doped BaCeO3 (BaCe0.90Y0.10O3−δ) has been studied by soft-X-ray spectroscopy. The valence band of H2-annealed BaCe0.90Y0.10O3−δ, which consists of the O 2p states hybridized with Ce 4f states, shifts to the higher binding energy side by approximately 0.4 eV. In the air-annealed BaCe0.90Y0.10O3−δ, holes and acceptor levels are observed at the top of the valence band and just above EF, respectively. Their intensities are lower in H2-annealed BaCe0.90Y0.10O3−δ. These findings indicate directly that hydrogen doping compensates for the presence of the holes.