Microstructural Evolution in a CeO2-Gd2O3 System
Abstract Microstructural evolution in a CeO2-Gd2O3 system at atomic and nanoscale levels with increasing Gd concentration has been comprehensively investigated by transmission electron microscopy. When the Gd concentration was increased from 10 to 80 at.%, the phase transformation from ceria with fluorite structure to solid solution with C-type structure was not a sudden change but an evolution in the sequence of clusters, domains, and precipitates with C-type structure in the fluorite-structured matrix. Moreover, the ordering of aggregated Gd cations and oxygen vacancies in these microstructural inhomogeneities developed continuously with increasing Gd concentration. This microstructural evolution can be further described based on the development of defect clusters containing Gd cations and oxygen vacancies.
Synthesis and Characterization of Nano-Hetero-Structured Dy Doped CeO2 Solid Electrolytes Using a Combination of Spark Plasma Sintering and Conventional Sintering
Doped ceria (CeO2) compounds are fluorite-type oxides that show oxide ionic conductivity higher than yttria-stabilized zirconia in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for low (500 degrees-650 degrees C) temperature operation of solid oxide fuel cells (SOFCs). To improve the conductivity in dysprosium (Dy) doped CeO2, nano-size round shape particles were prepared using a coprecipitation method. The dense sintered bodies with small grain sizes (< 300 nm) were fabricated using a combined process of spark plasma sintering (SPS) and conventional sintering (CS). Dy-doped CeO2 sintered body with large grains (1.1 mu m) had large micro-domains. The conductivity in the sintered body was low (-3.2 S/cm at 500 degrees C). On the other hand, the conductivity in the specimens obtained by the combined process was considerably improved. The micro-domain size in the grain was minimized using the present process. It is concluded that the enhancement of conductivity in dense specimens produced by the combined process (SPS+CS) is attributable to the microstructural changes within the grains.
Sintering behaviour and ionic conductivity of yttria-doped ceria
Abstract Highly sinterable yttria-doped ceria powder (YO1.5)x (CeO2)1 − x (x = 0.1–0.33) was fabricated by an optimized coprecipitation route. Compacted bodies could be sintered to impermeability at 1200 °C and near full density at 1300 °C, among the lowest temperatures reported for doped ceria densification. Ceria diffusion is important above 1400 °C. Excellent conduction properties were observed: high ionic conductivity (6.5 S m−1 at 750 °C for Ce0.8Y0.2O1.9), low activation energy (0.7 eV) and vanishing grain-boundary resistance.