Electrical conductivity properties of porous SmBaCo₂O_5+d and SmBa_0.5Sr_0.5Co₂O_5+d layered perovskite oxide systems for solid oxide fuel cell

In this study, the electrical conductivity characteristics of SmBaCo₂O_5+d (SBCO) and SmBa_0.5Sr_0.5Co₂O_5+d (SBSCO) were measured and analyzed by changing the characteristics of the microstructure from dense microstructure to porous microstructure for the cathode application in solid oxide fuel cells. SBCO and SBSCO comprised of the dense microstructure showed metal insulator transition (MIT) and metallic behavior, respectively. In SBCO, when the oxygen partial pressure is reduced, the conductivity value decreases, and the conductivity behavior changes to the behavior of a semiconductor. However, the electrical conductivity behavior of SBSCO did not change even when the oxygen partial pressure was decreased. The electrical conductivities of the porous cathodes were lower than those of the dense cathodes due to the discontinuous electric path, but all porous cathodes showed semiconductor behavior. The conductivity value decreases when the oxygen partial pressure decreases, but the general conductivity behavior of the samples with a porous microstructure does not change under N₂ atmosphere. The porous cathode showed the highest electrical conductivity when Pt lines were led to the top of the cathode. In this case, a relatively high electrical conductivity was measured using the method of measuring multiple conductivities at different temperatures while decreasing the measurement temperature starting from a high temperature rather than the method of measuring while raising the temperature starting from a low temperature. In the dense cathode, higher electrical conductivities were measured when a low current was applied, but in the porous cathode, the same electrical conductivity values were measured regardless of the applied current values.