Synthesis and preliminary study of NdxAE2-xMnO4±δ (AE: Ca, Sr) for symmetrical SOFC electrodes

NdxAE2-xMnO4±δ (AE: Ca, Sr) manganites with x = 0.25, 0.4, 0.5 and 0.60 are part of the Ruddlesden-Popper family of generic formula An+1BnO3n+1 with n = 1. The compositions range that can be successfully synthesized by the sol-gel method in air has been identified. While Sr compounds are stable in reducing atmosphere (3% H2/Ar - 850 °C/16 h), Ca ones decompose when submitted to such atmosphere. Nd0.5Sr1.5MnO4±δ was analyzed by High-Temperature X-ray diffraction (HT-XRD) showing TEC values of 12.7 × 10−6 K−1 and 14.4 × 10−6 K−1 in air and 3% H2/N2 (25-800 °C), respectively. Using standard conditions for electrode elaboration, the material reacts with YSZ electrolyte, but is chemically compatible with GDC electrolyte. A small polaron-type behavior is observed for the electrical conductivity of Nd0.5Sr1.5MnO4±δ in air and 3% H2/Ar, with respective values of 33.4 S cm−1 and 0.9 S cm−1 at 800 °C, meeting the preliminary requirements for use as symmetrical SOFC electrode.