XAFS study of the perovskite-type proton conductor SrZr_0.9Yb_0.1O_3-δ

Temperature dependence of XAFS spectra of the Perovskitetype proton conductor SrZr_0.9Yb_0.1O_3-δ at Sr and Zr K-edges and Yb L3, L2 and L1-edges have been investigated. Chemical shifts to lower energy and change in XANES spectra are observed with increasing temperature. No change in the XANES spectra and in the threshold energies of the Yb L3-, L2- and L1-edge was observed. This indicates that the effective charges (oxidation states) of the Sr and Zr ions change with oxygen loss while the effective charge of the Yb ions were maintained. The unit cell volumes increase with increasing temperature with a slight bend between 700 and 950 K. This bend of the unit cell volumes vs. temperature is considered to be due to the loss of oxygen, which is consistent with the result of a weight loss in TGA observed in the same temperature range. The mean-square relative displacements (MSRD) of the backscattering atoms with respect to the absorbing atom were also determined by EXAFS. Its temperature dependence increases with a slight bend between 700 and 950 K, which is considered to be due to a local structure change accompanied by the loss of oxygen rather than that by the phase transition at 948 K. It is proposed that the changes of local structure and effective charges of Sr and Zr ions must play an important role in the protonic conductivity.