EXAFS study of crystal structures of (Ba_1-xLa_x)₂In₂O_5+x and their oxide ion conductivity

Crystal structures of (Ba_1-xLa_x)₂In₂O_5+x (x=0.00, 0.20, 0.30, 0.40, 0.50) were analyzed by EXAFS and the powder X-ray Rietveld method. A Fourier transform of In K-edge EXAFS data from (Ba_1-xLa_x)₂In₂O_5+x showed a peak between 1.2 and 2.0 Å attributed to the nearest oxide ions around In³⁺ cation. The peak was back-Fourier transformed, and the structural parameters were refined by the least square fitting. The coordination number of In³⁺ cation increases with increasing La³⁺ cation content. This means oxygen is introduced at interstitial site by keeping an electroneutrality. As a result of the oxygen distribution, the oxide ion vacancies distribute randomly. The electrical conductivities of (Ba_1-xLa_x)₂In₂O₅ rapidly increased above 1203 K due to the order-disorder transition of oxygen vacancy. On the other hand, the electrical conductivities of (Ba_1-xLa_x)₂In₂O_5+x (x=0.20, 0.30, 0.35, 0.40, 0.45, 0.50) did not show the sharp discontinuity in the conductivity because the disorder phase of defective perovskite type structure was stabilized by doping La³⁺ cations at A-site even at low temperature.