Electronic conductivity measurement of Sm- and La-doped ceria ceramics by Hebb–Wagner method

Samarium- and lanthanum-doped ceria powders with compositions Ce0.8Sm0.2O1.9 (SDC) and Ce0.8La0.2O1.9 (LDC) were prepared by heating the oxalate solid solution (Ce0.8R0.2)2(C2O4)3 (R=Sm, La) at 873 K in air. As-prepared powders were densified to 96.3–97.4% relative density by sintering in air at 1773 K for 4 h. The electronic current of disk sample was measured at 1073 K for SDC and at 1113 K for LDC by direct current polarization method using Hebb–Wagner ion blocking cell. A linear relationship, which was theoretically predicted, was measured between log σe (electronic conductivity) and E (applied voltage) for both the samples in the applied voltage range of 0.01–1.0 V. The slopes of log σe–log PO2 (oxygen partial pressure) plot for both the samples agreed with the theoretically predicted value of −1/4 in the PO2 range from 102 to 10−5 Pa. In the PO2 range lower than 10−7 Pa, the slopes decreased to −1/7, which was close to the theoretical value of −1/6. In a high pressure range from 102 to 105 Pa, hole conduction with a slope of 1/4 was measured for LDC. The transport number of oxide ion for the SDC and LDC was significantly higher than the previously reported values.