A Study On The Electrochemical Properties Of ABO₃-Type Mixed Electronic-Ionic Conductor Materials

In this paper,three series of perovskite-type oxides Sm_xGd_0.5-xSr_0.5CoO_3-δ (SGSC),La_0.7Sr_0.3Co_1-yFe_yO_3-δ (LSCF) and La_0.8Sr_0.2Co_1-yFe_yO_3-δ (LSCF ) were synthesized by a low temperature combustion method. The synthesizing process and the phase of the SGSC and LSCF powders were characterized by TG-DSC and XRD, respectively. The morphology of the ceramics was characterized by SEM. The electrical conductivity of the ceramics was measured by the D.C. four-probe technique.The TG-DSC results indicated that the perovskite structure forms at 950℃for all SGSC samples and at 760℃for all LSCF samples. The XRD patterns showed that the SGSC powders are orthorhombic perovskite phase after sintered at 1200℃for 4h. The cell volume of SGSC increases with increasing Sm content. While the LSCF powders are hexagonal perovskite phase after sintered at 1250℃for 4h. The cell parameters increase with increasing Fe substitution.The SEM micrographs illuminated that a large number of pores exists in the SGSC ceramics after sintered at 1200℃for 4h. This should be ascribed to the liquid sintering. The grain size is about 3-5μm. The grain of LSCF reveals an orbicular polyhedron profile, with a dimension about 3-5μm.The electrical conductivity measurement results for the Sm_xGd_0.5-xSr_0.5CoO_3-δ samples showed that Sm content has an important influence on the electrical conductivity of SGSC. At 500℃, the electrical conductivity is increased from 818.7 S·cm^-1 for Gd_0.5Sr_0.5CoO_3-δ to the maximum value 1820.8S·cm^-1 for Sm0.3Gd0.2Sr_0.5CoO_3-δ, then decreased to 1115.7 S·cm^-1 for Sm_0.5Sr_0.5CoO_3-δ. In addition, the electrical conductivities for SGSC reveal different temperature-dependence behavior. The electrical conductivity of Gd_0.5Sr_0.5CoO_3-δ increases with increasing temperature, indicating a semiconductor conducting behavior. While the electrical conductivities of the other samples decrease with increasing temperature, implying a metallic conducting behavior. The electrical conductivity measurement results for the LSCF samples showed that the conductivities of La_0.7Sr_0.3Co_1-yFe_yO_3-δ are higher than those of La_0.8Sr_0.2Co_1-yFe_yO_3-δ. For the LSCF with y=0, the electrical conductivities decrease with increasing temperature, obeying to a metallic conducting behavior. For the other samples, the electrical conductivities increase with temperature, following the semiconductor conducting behavior.