Effect of alumina addition on the electrical and mechanical properties of Ce_0.8Gd_0.2O_2-δceramics

(1-x) Ce0.8Gd0.2O2 - δ+ x Al2O3ceramics with compositions x = 0 to 0.2 were prepared by the conventional mixed-oxide method from high purity (>99.9%) of commercial powders, and sintered at 1550 °C for 5 h in air. Sintered density, crystal phase, and microstructure were characterized. The ionic conductivity was measured over 200 to 800 °C in air using an impedance analyzer in the frequency range of 0.001 to 100 Hz. Microhardness and indentation fracture toughness were also determined. A new phase (i.e., GdAlO3) has been detected in the samples with Al content greater than 5% AlO1.5. Ce0.8Gd0.2O2-δceramic has a Vickers hardness of ∼ 9.23 ± 0.15 GPa, and an indentation fracture toughness of ∼ 1.47 ± 0.2 MPa m1/2. A remarkable improvement in both fracture toughness and microhardness can be observed for the samples with over 10% AlO1.5. However, the addition of Al2O3exhibits a detrimental effect on the conductivities, especially on grain boundary conductivity, which is possibly related to the formation of GdAlO3.