Influence of erbia or europia doping on crystal structure and microstructure of ceria–zirconia (CZ) solid solutions

In this study we have prepared three zirconia–ceria compositions, namely 12, 50 and 80 mole% CeO2. Along with each pure ceria–zirconia composition we have prepared two parallel erbia- or europia-doped materials in which 0.5 mole% of each of the two starting oxides is replaced by 1 mole erbia or europia. We observed that the microstructures of CZ12 samples are fairly homogeneous in grain size distribution, while those doped with erbia or europia present large as well as small grains, but smaller average size than pure CZ12. Pure CZ50 solid solution showed the presence of two tetragonal phases whereas CZ50-Er and CZ50-Eu show the presence of two phases if sintered below 1450 °C, but only one above 1450 °C. The grains of CZ50 and CZ50-Er have wavy borders and faceting, whereas those of CZ50-Eu have rounded borders and faceting is not greatly displayed. CZ80 series showed the cubic fluorite structure for any sintering cycle, but the addition of europia reduces the grain size with respect to the pure CZ80 and to the parallel erbia-doped solution.