Consolidation and properties of Gd_0.1Ce_0.9 O_1.95 nanoparticles for solid-oxide fuel cell electrolytes

Gd-doped ceria solid solutions have been recognized to be leading electrolytes for use in intermediate-temperature fuel cells. In this paper, the preparation, solubility, and densification of Gd_0.1Ce_0.9O_1.95 ceramics derived from carbonate co-precipitation are reported. The dissolution of Gd₂O₃ in CeO₂ lattice was identified to be completed during the co-precipitation process by studying the lattice parameter as a function of temperature. After calcination at 800 °C for 2 h, the nano-sized Gd_0.1Ce_0.9O_1.95 powder (∼33 nm) with a nearly spherical shape and a narrow particle-size distribution was obtained. This calcined powder has high sinterability and maximum densification rate at ∼1000 °C. Sintering at 1300 °C for 4 h yielded over 97% relative density with near maximum. The grain size increased with increases in sintering temperature. The ionic conductivity of these pellets was tested by alternating current impedance spectroscopy to elucidate the contribution of intragranular and intergranular conductivity to the total ionic conductivity. It was found that sintering temperature does not affect intragranular conductivity, though intergranular conductivity was strongly influenced by grain size, grain boundary area, and relativity density. This pellet sintered at 1500 °C for 4 h showed a high ionic conductivity of 5.90 × 10^-2 s/cm when measured at 750 °C. The characterization and structural evaluation of the as-received powders were carried out using x-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller, and dilatometer and impedance analysis. © 2006 Materials Research Society.