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Ionic conductivities of CeO₂:Y₂O₃ bulk ceramic were investigated with different sintering temperatures and correlated with the resulted microstructure. Lower sintering temperatures (T≤1400°C) were found to give much higher overall DC conductivities (e.g., σ_DC∼7×10⁻³ S/cm at 700°C for a 4% Y₂O₃-doped sample sintered at 1400°C). The samples sintered at lower temperatures showed higher grain boundary conductivities than those sintered at the traditional sintering temperature, 1500°C. The model involving non-resistive grain boundaries can be employed to explain the lower grain boundary resistivities in our samples of low sintering temperatures. These samples were examined by scanning transmission electron microscopy (STEM) with energy dispersive X-ray (EDX) and electron energy loss spectroscopy (EELS). Most of the boundaries (>90%) were found precipitate-free in the small grain samples, and a …