Structural study of a sol–gel derived novel solid oxide fuel cell perovskite: (La1−xSrx)(Cr0.85Fe0.05Co0.05Ni0.05)O3−δ

The effect of composition on the structure of the new solid oxide fuel cell (SOFC) perovskite (La 1− x Sr x )(Cr 0.85 Fe 0.05 Co 0.05 Ni 0.05 )O 3−δ is studied using x-ray diffractometry, pycnometry, and Fourier-transform infrared and Raman spectroscopy. Samples were synthesized using the Pechini method via doping the La site with Sr 2+ , to a composition with x = 0–0.4 mole fraction, and at the Cr site with 0.05 mol of Co 2+ ,Fe 2+ and Ni 2+ , and the structural results were compared with those for orthorhombic LaCrO 3 . The samples were orthorhombic perovskite of the Pnma space group. A second phase, monoclinic SrCrO 4 , was also observed, whose content increased linearly with increasing x . A large decrease in the lattice and hence volume was observed for the sample with x = 0.1, which was accompanied by a sharp decrease in the Cr−O bond length, tilt angle and crystallite size. The structural parameters were almost invariant for x = 0.1–0.4, probably due to an increase in content of the high valence cations of smaller ionic radii, as suggested by an increase in the intensity of the defect band (∼515 cm −1 , IR). The octahedral CrO 6 stretching, bending and tilting modes were found shifted accordingly. A mechanism employing a partial-charge model was proposed to explain the results.