Electrical Properties of Nb-Doped SrTiO[sub 3] Ceramics with Excess TiO[sub 2] for SOFC Anodes and Interconnects

The electrical properties of Nb-doped ceramics with and without excess were investigated for anodes and interconnects of SOFCs by a dc four-probe conductivity measurement. The microstructures and the grain boundary properties were revealed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, SEM–electron backscatter diffraction pattern-orientation imaging microscopy, and high-resolution transmission electron microscopy. It was found that the conductivity of Nb-doped polycrystal was semiconductor-like with positive temperature coefficient while the single crystal and the polycrystal with excess showed the conductivity with negative temperature coefficient-like metals at SOFCs operating temperatures. The second phases was found in the polycrystal materials with excess . No grain boundary segregation was found, and the excess was found to stay at the triple grain junctions. The grain-boundary orientation was found mostly random either with or without excess . These results suggest that the excess reduces the influence of the grain boundary on the conduction.