Multielectronic conduction in La1−xSrxGa1/2Mn1/2O3−δ as solid oxide fuel cell cathode

Four-probe dc conductivities, capacitances, and thermopower have been measured in the temperature range of 80–1123 K for La1−xSrxGa1/2Mn1/2O3−δ, which is a desirable cathode material for lanthanum–gallate electrolytes of solid oxide fuel cells. The dc conductivities in the specimens (0.1⩽x⩽0.3) are insensitive to x but the thermopower is very sensitive to x, although the x=0 specimen exhibits a somewhat different conduction behavior. At T<300 K, a relaxation process has shown in dielectric loss factor with the activation energy higher than that for dc conduction in every specimen. These results at T<300 K have been numerically analyzed within the framework of the multielectronic conduction consisting of the polaronic conduction of Mn 3d eg holes created by Sr doping, the band conduction of O 2p holes and the hopping conduction of Mn 3d eg electrons, where the O 2p holes and Mn 3d eg electrons are created by thermal excitation of electrons from O 2p bands to Mn 3d eg narrow bands. At T>500 K, the band conduction dominates the electronic transports. The ionic conduction due to O2− migration seems difficult to contribute directly to the dc conduction even at high temperature.