A series of Y0.2 Zrx Ce0.8−x O1.9 compounds (0 ≤ x ≤ 0.6) had been prepared by the modified sol-gel method and characterized by powder X-ray diffraction, thermo-gravimetric analysis, four-probe resistivity, and Vickers’s hardness studies. The gels from co-precipitation were treated with heated 1-octanol. All of the samples showed fluoride structure after calcined at 600 °C. Sintering the powders of Y0.2 Ce0.8 O1.9 and Y0.2 Zr0.6 Ce0.2 O1.9 at 1300 °C gave the relative density of 95.8% and 99%, respectively. 99% relative density could be obtained for all samples after sintering at 1500 °C. This study showed a much more improved result than that of the previous reports. The hardness was 13.7 GPa for the Y0.2 Zr0.6 Ce0.2 O1.9 pellet, which was twice greater than that for Y0.2 Ce0.8 O1.9 (7.1 GPa). Therefore, the mechanical properties could be improved by the addition of ZrO2 to Y0.2 Zrx Ce0.8−x O1.9 . At 800 °C, the electrical conductivity of Y0.2 Ce0.8 O1.9 and Y0.2 Zr0.6
Ce0.2 O1.9 were 3.3 × 10−2 S/cm and 5.5 × 10−3 S/cm, respectively. The conductivity was decreased by the addition of ZrO2 to Y0.2 Ce0.8 O1.9 . It showed that the conductivity and hardness of Y0.2 Zr0.2 Ce0.6 O1.9 were 1.2 × 10−2 S/cm and 9.6 GPa, respectively, at 800 °C and could be a better electrolyte candidate for “intermediate-temperature” unitized regenerative solid oxide fuel cells.