Oxides of lanthanum(1-x) strontium(x) cobalt(1-y) iron(y) oxygen(3) for oxygen and electrical delivery systems

Perovskite-type compounds in the system {dollar}rm Lasb{lcub}1-x{rcub}Srsb{lcub}x{rcub}Cosb{lcub}1-y{rcub}Fesb{lcub}y{rcub}Osb{lcub}3-delta{dollar} have been considered as potential cathode materials for solid oxide fuel cells. The purpose of this study was to evaluate the structural, electrical, thermochemical properties of these compositions.; The first and second papers of this dissertation dealt with the material synthesis, crystal structure, thermal expansion, thermogravimetry, electrical conductivity, and thermoelectricity of {dollar}rm Lasb{lcub}0.8{rcub}Srsb{lcub}0.2{rcub}Cosb{lcub}1-y{rcub}Fesb{lcub}y{rcub}Osb3{dollar} (y = 0-1) and {dollar}rm Lasb{lcub}1-x{rcub}Srsb{lcub}x{rcub}Cosb{lcub}0.2{rcub}Fesb{lcub}0.8{rcub}Osb3{dollar} (x = 0-1) in air, respectively. Electrical conductivities and thermal expansion coefficients for these compositions were found to increase with Sr and Co contents. The unique temperature and composition dependence of the electrical conductivity observed in both systems were semi-empirically modeled by incorporating several mechanisms which include the hopping conduction of small polarons, a thermally activated charge disproportionation of Co{dollar}sp{lcub}3+{rcub},{dollar} the ionic compensation by oxygen vacancy, and a preferential electronic compensation of acceptor by forming Fe{dollar}sp{lcub}4+{rcub}{dollar} over Co{dollar}sp{lcub}4+{rcub}.{dollar}; Phase stability, oxygen content, electrical conductivity, and Seebeck coefficient of {dollar}rm Lasb{lcub}1-x{rcub}Srsb{lcub}x{rcub}Cosb{lcub}0.2{rcub}Fesb{lcub}0.8{rcub}Osb{lcub}3-delta{rcub}{dollar} (x = 0, 0.2, 0.4) as function of temperature and oxygen activity were reported in the third paper. Both the oxygen deficiency and phase stability of compositions with y = 0.8 were found considerably high. It has been demonstrated that the degree of oxygen deficiency in these compositions significantly influences their structural and electrical properties, especially in the high temperature region.