ELECTRICAL PROPERTIES OF Sr_(0.86)Y_(0.08)TiO_3 UNDER REDOX AND FULL CELL FABRICATION CONDITIONS

摘要

The effects of manufacturing and preparation conditions on the structural and electrical properties of Sr_(0.86)Y_(0.08)TiO_3 (SYT) reduced in 5% NH_3 (95% N_2) are discussed. The realization of an SYT-based SOFC anode is challenging because the conductivity of SYT is highly dependent upon the thermal history combined with heat treatment atmosphere used in manufacturing. To obtain highly conductive SYT as a candidate for an SOFC anode material, all samples in this study were pre-reduced to 1400℃ under reducing conditions (ammonia) for 8 hours. After pre-reduction, 3 samples were oxidized in air at 850℃, 950℃ and 1050℃, respectively, for 4 hours to evaluate the impact of oxidizing conditions in practical cell fabrication processes on the SYT conductivity. XRD analyses showed that the lattice parameter of SYT sintered in ammonia was slightly different than the sample sintered in air. Measured at 800℃ in reducing atmosphere (dry N_2/4%H_2), the maximum electrical conductivity of 36.3 S/cm was observed in SYT reduced in ammonia at 1400℃. However, the observed conductivities were not preserved after oxidation-reduction cycles. Various SYT samples pre-reduced in ammonia at 1400℃ and then oxidized in air at 850℃, 950℃ and 1050℃ showed an irreversible drop on conductivity measured in a reducing atmosphere, and the higher the oxidation temperature, the lower the conductivity became. The conductivity results indicate a strong dependence upon the SYT manufacturing and processing conditions. Despite the irreversible drop due to the oxidation cycle, the conductivity of SYT sintered in ammonia at 1400℃ is still reasonable as a candidate for SOFC anodes, with careful management of cell fabrication conditions to avoid any oxidation processes at temperatures above 1050℃.