Substitution induced B-cation ordering in solid oxide fuel cell ceramics: (La0.8Sr0.2)(M0.9Ni0.1)O3 (M = Mn, Cr)

Perovskites are important materials in a number of important technological applications, including solid oxide fuel cells, catalysis, and giant magneto-resistance materials. For many of these purposes, a mixture of B-cations can be used to tune the desired properties, e.g., oxygen reduction, ionic conductivity. For a solid oxide fuel cell, two particular ceramic components are of critical importance and have been extensively studied, the cathode (La0.8Sr0.2)MnO3−x and the interconnect material (La0.8Sr0.2)CrO3. In this study, we examined the mixed B-cation perovskites (La0.8Sr0.2)(M0.9Ni0.1)O3 (M = Mn, Cr). All materials were synthesized using the glycine-nitrate method, followed by air annealing. The structures were determined using powder neutron diffraction methods. Refinement of the data showed that even at this low concentration, the compounds have monoclinic symmetry (P21/n) and that the nickel had a strong preference for the smaller of the two octahedral sites. This small amount of nickel substituted on the B-site resulted in a symmetry reduction when compared to the unsubstituted (LaSr)MnO3 or (LaSr)CrO3 materials. Although this structural type has been seen previously in heavily substituted perovskites, these materials show that even at this low level of substitution a segregation of the metals in a manner similar to the double perovskites A2BB′O6−x can be detected. This may have implications involving material stresses on cycling that may result as the temperature is raised or lowered through this crystallographic transition.