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 (La1-xSrx)(Cr0.85Fe0.05Co0.05Ni0.05)O3-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 Sr2+, to a composition with x = 0-0.4 mole fraction, and at the Cr site with 0.05 mol of Co2+,Fe2+ and Ni2+, and the structural results were compared with those for orthorhombic LaCrO3. The samples were orthorhombic perovskite of the Pnma space group. A second phase, monoclinic SrCrO4, 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 CrO6 stretching, bending and tilting modes were found shifted accordingly. A mechanism employing a partial-charge model was proposed to explain the results