Local electronic structures around hydrogen and acceptor ions in perovskite-type oxide, SrZrO3

Local electronic structures around hydrogen and acceptor ions in SrZrO3 are simulated by the DV-Xα molecular orbital method. In pure SrZrO3, there is a band gap of about 6 eV between the O–2p valence band and the Zr–4d conduction band, in agreement with experiments. When Y or Sc is doped into SrZrO3, an acceptor level appears just above the valence band. When hydrogen is introduced into SrZrO3, a donor level appears below the conduction band. Also, an oxygen ion vacancy makes the defect level below the conduction band. It is shown that charge compensation takes place among these acceptor, donor and defect levels. In addition, local electronic structure around hydrogen is found to change largely with the acceptor dopants, Sc and Y. For example, the metal–oxygen bond strength changes in the order, Y–O<Zr–O<Sc–O, which probably modifies the thermal vibrational amplitude of oxygen ions near hydrogen, and affects protonic conductivity in the doped SrZrO3.