A Study of the Defect Structure of Nonstoichiometric CeO2

Abstract

The electrical conductivity of arc cast specimens of Ce1+yOx have been measured as a function of temperature and oxygen pressure. These preliminary results indicate that although the absolute value of the conductivity for arc cast Ce1+yO2 specimens differs from the sintered specimens the temperature and oxygen pressure behavior is similar. The electron mobility in Ce1+yO2 was calculated from the electrical conductivity and thermodynamic data and the assumption that the atomic defects exist predominantly in only one state of ionization. The data for the calculations in the temperature range 800° - 1200°C was selected from the oxygen pressure region where according to the analysis of the conductivity data the predominant defects are electrons localized on normal cerium ions and quadruply ionized cerium interstitials. The calculated electron mobilities of sintered and arc cast Ce1+yO2 specimens increase exponentially with increasing temperature between 800° and 1200°C. Based on the temperature dependence of the mobility, the electron conduction mechanism appears to be a hopping type process with an activation energy of 0.14eV. The magnitude of the mobility is of the order of 10-2 cm2/v-sec. A galvanic cell using a commercially made calcium stabilized zirconia tube was used to measure the PO2 of analyzed and premixed gas mixtures of Ar-02 and CO-CO2 over a wide range of oxygen pressures near 1000°C. The accuracy of the cell was evaluated by comparing these results with the reported analyses of these mixtures. A model based on thermal diffusion was used to explain the variation of the emf with flow at low flow rates. Errors due to a temperature difference across the electrolyte were also evaluated. When properly employed this cell has been shown to be a sensitive research device for the accurate measurement of the PO2 over a wide range