Preparation and characterization of perovskite-type Ln′Ln″_1-xCoO₃ for electroceramic applications

Heteronuclear complexes of the type Ln′Ln″_1-x[Co(CN)₆]·nH₂O have been synthesized for potential applications in solid oxide fuel cells. Sm_xE_1-xCo and Sm_xYb_1-xCo complexes crystallize in the orthorhombic system, as do La_xSm_1-xCo 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′ + (1-x)r_Ln″] shows linear behaviour similar to that observed for the LnCo complexes. For the decomposed products, perovskite-type Ln′_xLn″_1-xCoO₃ oxides are obtained. The crystal structure of Ln′_xLn″._1-xCoO₃ 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.