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A cylindrical Li 7 La 3 Zr 2 O 12 specimen in contact with an Al 2 O 3 crucible is sintered and the effect of Al diffusion on the microstructure, phase composition, and Li-ion conductivity of Li 7 La 3 Zr 2 O 12 is investigated. The decrease in the Li-ion conductivity and Al concentration with increasing distance from the contact area with the Al 2 O 3 crucible is confirmed using spatially resolved local-impedance spectroscopy and compositional analysis. The region close to the Al 2 O 3 crucible shows abnormally large grains (size > 0.7 mm) within a matrix of fine grains (size: ∼10 μm), abundant intergranular liquid, the Li 7 La 3 Zr 2 O 12 phase mostly in cubic form, and a high Li-ion conductivity (8.5 × 10 −5 S cm −1 ). In contrast, the region far from the Al 2 O 3 crucible exhibits uniform fine grains (size: ∼10 μm), scarce intergranular liquid, the tetragonal form of the Li 7 La 3 Zr 2 O 12 phase, and a low Li-ion conductivity (1.1 × 10 −6 S cm −1 ). The incorporation of Al into the Li 7 La 3 Zr 2 O 12 lattice and the resulting increase in the number of Li-ion vacancies is suggested to be the main reason for the increase in the Li-ion conductivity. The origins of the abnormal grain growth induced by the diffusion of Al are discussed in relation to the atomic surface structures of Li 7 La 3 Zr 2 O 12 and the presence of intergranular liquid phase.

Gadolinia-doped ceria (GDC, Gd0.1Ce0.9O1.95) powders with high sinterability are prepared by carbonate coprecipitation and applied in the fabrication of Ni–YSZ (yttria-stabilized zirconia)-supported tubular solid oxide fuel cells (SOFCs) with a cell configuration of Ni–YSZ/Ni/Ni–GDC/GDC/LSCF(La0.6Sr0.4Co0.2Fe0.8O3−δ)–GDC/LSCF. A high power density (594 mW cm−2) at 600 °C is achieved using the cell (diameter: 6 mm) prepared by sintering of the electrolyte at 1400 °C. This result is attributed to the dense electrolyte and good adherence between GDC and the electrode. The carbonate-derived GDC powders can be sintered to 97% of the theoretical density even at 1050 °C, which demonstrates that the fabrication temperature of tubular SOFCs can potentially be lowered by using cost-effective Ni–YSZ supports.