The effects of transition metal oxide doping on the sintering of cerium gadolinium oxide

The effects of two transition metal oxide dopants, Co and Cr, on the densification properties of Ce0.9Gd0.1O1.95 (CGO) have been examined. While a low concentration of Co oxide was found to reduce the sintering temperature of CGO by over 150 °C, the addition of Cr oxide, at concentrations greater than 0.1 cat.%, was found to be detrimental to the densification of the material. Energy-dispersive X-ray (EDX) spectrum imaging was used to examine the elemental evolution in both materials. At ∼70% relative density, a continuous transition-metal-oxide-rich film was located around the primary crystallites in both materials. With increasing relative density, the concentration of both dopants was shown to decrease without there being a considerable change in the apparent grain boundary layer thickness. All specimens examined revealed considerable grain boundary Gd enrichment and Ce depletion, with this effect becoming more pronounced with increasing relative density in the Cr-doped CGO. EDX spectrum imaging performed on the high density specimens revealed the presence of discrete second phases in both materials, which were subsequently analysed by electron energy loss spectroscopy. Using the current set of results, mechanisms responsible for the modified densification behaviour in Co-doped and Cr-doped CGO are suggested.