Manganese-rich SmBaCo2−x−yMnxMgyO5+δ (x = 0.5, 1, 1.5 and y = 0.05, 0.1) with stable structure and low thermal expansion coefficient as cathode materials for IT-SOFCs

SmBaCo2−x−yMnxMgyO5+δ (x = 0.5, 1, 1.5 and y = 0.05, 0.1) samples are synthesized by sol-gel method. The influence of different substitution of Mn and Mg for Co on crystal structures, thermal expansion coefficient (TEC), electrical conductivities and electrochemical performances have been investigated. The generation of the secondary phase BaMnO3 is suppressed with Mg2+ increasing. Demonstrated by temperature-dependent X-ray diffraction from 25 °C to 700 °C, the structure of SmBaCo0.4Mn1.5Mg0.1O5+δ in high temperature is stable. The TEC of SmBaCo1.45Mn0.5Mg0.05O5+δ, SmBaCo0.95MnMg0.05O5+δ, SmBaCo0.45Mn1.5Mg0.05O5+δ and SmBaCo0.4Mn1.5Mg0.1O5+δ are 15.77 × 10−6 K−1, 16.20 × 10−6 K−1, 12.19 × 10−6 K−1 and 12.58 × 10−6 K−1, respectively, which are much lower than those of cobalt-based layered perovskites and more compatible with the thermal expansion of SDC electrolyte. Although the electrochemical performances of SmBaCo2−x−yMnxMgyO5+δ (x = 0.5, 1, 1.5 and y = 0.05, 0.1) decrease slightly with Mn increasing, the polarization resistances of the SmBaCo1.45Mn0.5Mg0.05O5+δ and SmBaCo0.4Mn1.5Mg0.1O5+δ are 0.17 Ω cm2 and 0.30 Ω cm2 at 800 °C, respectively, which can meet the electrochemical performance requirements of cathode materials. Among the samples, the SmBaCo1.45Mn0.5Mg0.05O5+δ and SmBaCo0.4Mn1.5Mg0.1O5+δ show better tradeoff properties between TEC and electrochemical performance as cathode materials for IT-SOFCs.