Preparation and characterization of perovskite-type Ln′xLn″1–xCoO3 for electroceramic applications

Abstract

Heteronuclear complexes of the type Ln′_xLn″_{1 –x}[Co(CN)₆]·nH₂O have been synthesized for potential applications in solid oxide fuel cells. Sm_xEr_{1 –x}Co and Sm_xYb_{1 –x}Co complexes crystallize in the orthorhombic system, as do La_xSm_{1 –x}Co complexes for x= 0-0.6. A plot of the lattice parameters of the orthorhombic structures of the complexes as a function of r_eff[xr_Ln′+(l -x)r_Ln′] shows linear behaviour similar to that observed for the LnCo complexes. For the decomposed products, perovskite-type Ln′_xLn″_{1 –x}CoO₃ oxides are obtained. The crystal structure of Ln′_xLn″_{1 –x}CoO₃ is orthorhombic for 0.1080 < r_eff/nm < 0.1199 and hexagonal for r_eff > 0.1199 nm, while for r_eff < 0.1080 nm no perovskite-type oxide was formed. We suggest that the orthorhombic distortion parameter is greater than ca. 0.267 for r_eff < 0.1080 nm and therefore no perovskite-type oxide is formed.