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 sigma(e) (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 sigma(e)-log PO2 (oxygen partial pressure) plot for both the samples agreed with the theoretically predicted value of -1/4 in the PO2 range from 10(2) 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 10(2) to 10(5) 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. (C) 2004 Elsevier B.V. All rights reserved.