Microstructure of cobalt oxide doped sintered ceria solid solutions

The sintering of ceria solid solutions, such as Ce0.9Gd0.1O1.95 (CGO10), is strongly promoted by the addition of 1 cat% of cobalt oxide, lowering the maximum sintering temperature by 200 degrees C and triplicating the maximum densification rate. This change in sintering behavior results from cobalt ion segregated at the grain boundaries. An average cobalt ion boundary coverage is at maximum 3.0 +/- 1.9 at/nm(2) and is shown to depend on the cooling rate. Coverage by segregated gadolinium is also found and amounts to 13.2 +/- 11.4 at/nm(2) for a slowly cooled sample. From cobalt excess measured at the boundary, an estimated concentration of only 0.06 cat% of cobalt oxide is necessary to promote the sintering effect. The remaining amount of cobalt oxide is found in triple points and as particles in clusters. It is expected that the amount of cobalt oxide necessary for fast densification can be reduced with a doping process that distributes the additives more homogeneously.