2009 Volume 117 Issue 1361 Pages 60-65
Phase relationship of Ba2-xLaxIn2O5+δ has been investigated by using dilatometry, differential scanning calorimetry and synchrotron X-ray diffraction at high temperatures. Decrease of the temperature of the first order phase transition, from brownmillerite orthorhombic to tetragonal, was observed with an increase of La content in Ba2-xLaxIn2O5+δ for x = 0.0-0.2, whereas little variation was detected on temperature of the second order phase transition, from tetragonal to distorted cubic, in the specimens with x = 0.0-0.3. Ba2-xLaxIn2O5+δ with x larger than 0.4 showed no phase transition by temperature. Crystal structure of the specimens with 0.4 ≤ x ≤ 1.0, 1.2 ≤ x ≤ 1.7 and x = 2.0 were ideal cubic, tetragonal and orthorhombic distorted perovskite, respectively. Ba1.3La0.7In2O5+δ with ideal cubic perovskite structure showed higher oxide ion conductivity below 800°C than that of Ba2In2-xGaxO5 with distorted cubic structure, supporting that removal of the structural distortion should be effective to improve mobility of oxide ion, resulting in as high oxide ion conductivity as that of yttria stabilized zirconia.