Crystal structure and high-temperature electrical conductivity of novel perovskite-related gallium and indium oxides

Novel complex oxides Sr 2 Ga 1+ x In 1− x O 5 , x = 0.0–0.2 with brownmillerite-type structure were prepared in air at T = 1,273 K, 24 h. Study of the crystal structure of Sr 2 Ga 1.1 In 0.9 O 5 refined using X-ray powder diffraction data (S.G. Icmm , a = 5.9694(1) Å, b = 15.2091(3) Å, c = 5.7122(1) Å, χ 2 = 2.48, R F 2 = 0.0504, R p = 0.0458) revealed ordering of Ga 3+ and In 3+ cations over tetrahedral and octahedral positions, respectively. A partial replacement of Sr 2+ by La 3+ according to formula Sr 1− y La y Ga 0.5 In 0.5 O 2.5+ y /2 , leads to the formation of a cubic perovskite ( a = 4.0291(5) Å) for y = 0.3. No ordering of oxygen vacancies or cations was observed in Sr 0.7 La 0.3 Ga 0.5 In 0.5 O 2.65 as revealed by electron diffraction study. The trace diffusion coefficient ( D T ) of oxygen for cubic perovskite Sr 0.7 La 0.3 Ga 0.5 In 0.5 O 2.65 is in the range 2.0 × 10 −9 –6.3 × 10 −8 cm 2 /s with activation energy 1.4(1) eV as determined by isotopic exchange depth profile technique using secondary ion mass spectrometry at 973–1,223 K. These values are close to those reported for Ca-doped ZrO 2 . High-temperature electrical conductivity of Sr 0.7 La 0.3 Ga 0.5 In 0.5 O 2.65 studied by AC impedance was found to be nearly independent on oxygen partial pressure. Calculated values of activation energy at T < 1,073 K for hole and oxide-ion conductivities are 0.96 and 1.10 eV, respectively.