Crystal structure, oxygen nonstoichiometry, and conductivity of mixed ionic-electronic conducting perovskite composites with CeO₂

Conductivity, structure, and oxygen nonstoichiometry of compositions in the following series (100 - x) La_0.6Sr_0.4CoO _3±δ.xCeO₂ (LSCCe) and (100 - x) La _0.6Sr_0.4CoO_3±δ.xCeO₂ (LSMCe), where x = 0, 2, 5, and 10 mol %, are studied. CeO₂ has a low solubility limit in the rhombohedral structure. Compositions containing more than 2 mol % ceria are two-phase and consist of a perovskite constituent with rhombohedral structure and ceria with cubic structure. Small additions of CeO₂ influence the conductivity of the modified perovskites in a different way. The conductivity in the LSCCe series dramatically decreases with an addition of up to 10 mol % CeO₂. However, the total conductivity in the LSMCe series only changes slightly. The conductivity of the perovskites as a function of oxygen partial pressure (0.21 to 1 × 10^-4 atm) is discussed. Oxygen nonstoichiometry (δ) depending on temperature and oxygen partial pressure varies in the LSCCe series in a wider range (0<δ < 0.23) compared to that in the LSMCe series (0.06<δ <0.14). In contrast to the LSMCe series, the compositions in the LSCCe series show a strong relationship between lattice parameters, oxygen nonstoichiometry, and conductivity. X-ray photoelectron spectroscopy indicates that distortion of Co-O bonds takes place, which could affect electronic conductivity of perovskites.