Abstract
The effect of composition on the structure of the new solid oxide fuel cell (SOFC) perovskite (La1-xSrx)(Cr0.85Fe0.05Co0.05Ni0.05) O3-delta 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 (similar to 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.