Doped ceria solubility limits

The conductivities of some ceria-containing compounds obtained from the literature have been compiled and shown as solid lines in Fig. 2.12. The main dopants for ceria belong to the alkaline earth or rare-earth metal series and the majority of doped samples exhibit conductivity values which fall into a rather limited band (gray band in Fig. 2.12), which points to a similar behaviour for all doped ceria samples. Exceptions are pure ceria and ceria doped with redox elements like Pr and Tb which give rise to electronic contribution to conductivity. An important requirement is that a homogeneous solid solution forms between the two oxides, which maintains the fluorite structure since the presence of a second phase or phase inhomogeneity due to insufficient solubility can affect ionic conductivity. The very low values of conductivity found for BaO and MgO-doped ceria were in fact attributed to the low solubility of these oxides into the lattice of When the... 

La-doped ceria. A correlation between synthesis process, nanodomain size, and total ionic conductivity was observed for Yb, Ho, and Dy -doped ceria. Furthermore, recent results question the established solubility limits of rare-earth cations in ceria. Although the lattice parameter of ceria increases with La doping up to 40 mol% LaOi the true solubility turns out to be below 20 mol% LaOj 5 as evidenced from the formation of C-LagOg after annealing Ceo.sLao.aOi g at 1000 °C for 7 days. Pronounced deviations from Vegard s law have been consistently observed for the lattice constant of Gd-doped ceria. These may be rationalized by the formation of C-GdgOg domains within the ceria fluorite lattice. ... 

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