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.
Influence of nano-structural feature on electrolytic properties in Y2O3 doped CeO2 system
Abstract Doped ceria (CeO2) compounds are fluorite type oxides which 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 temperature operation (500–650 8C)’ of solid oxide fuel cells (SOFCs). In this study, YxCe12xO22d (x ¼ 0:05; 0:1; 0:15; 0:2 and 0.25) fine powders were prepared using a carbonate co-precipitation method. The relationship between electrolytic properties and nano-structural features in the sintered bodies was examined. The micro-structures of Y0.05Ce0.95O1.975, Y0.15Ce0.85O1.925 and Y0.25Ce0.75O1.875 as representative three specimens have been investigated in more detail with transmission electron microscopy (TEM). The big diffuse scattering was observed in the background of electron diffraction pattern recorded from Y0.15Ce0.85O1.925 and Y0.25Ce0.75O1.875 sintered bodies. This means that the coherent micro-domain with ordered structure is in the micro-structure. While Y0.25Ce0.75O1.875 sintered body with low conductivity and high activation energy has big micro-domains, the micro-domain size in Y0.15Ce0.85O1.925 with high conductivity and low activation energy was much smaller than that of Y0.25Ce0.75O1.875. TEM observation gives us message that the size of coherent micro-domain with ordered structure would closely relate to the electrolytic properties such as conductivity and activation energy in the specimens. It was concluded that a control of micro-domain size in nano-scale in Y2O3 doped CeO2 system was a key for development of high quality solid electrolyte in fuel cell application. © 2003 Elsevier Ltd. All rights reserved.
Superfast densification of oxide ceramics by spark plasma sintering
The SPS (Spark Plasma Sintering) Process is a new materials synthesis procussing techllology recently developed by Sumitomo Coal Mining Co.Ltd.. Japan. Some oxides such as Al2O3, Y-TZP,YAG, Al2O3-ZrO2 and Mullite were successfully superfast densified by SPS under the conditions of heating rate as high as 600℃/min, no keeping time at the sintering temperatures above 1200℃,and thed fast cooling to 600℃ within 3 minutes. The superfast sintering samples show high densities, fine inicrostructures and excellent mechanical properties. The fracture toughness K1c of 20mol% Al2O3-ZrO2 (3Y) samples sinterse by SPS at 1250℃ for 2 min is higher than 6MPa.m1/2.The reaction sintering of ZrO2- mullitc could be completed by SPS at 1530℃ for 3 min.