THE IMPURITY EFFECTS AND THE NONSTOICHIOMETRIC DEFECT CHARACTERIZATION OF CERIUM OXIDE(2-X) AND CERIUM(.9)ZIRCONIUM(.1)OXIDE(2-X) IN THE NEAR-STOICHIOMETRIC COMPOSITION RANGE
Abstract
The electrical conductivity of CeO(,2-x) was measured in the temperature range 800(DEGREES) - 1000(DEGREES)C and 1-10('-3) atm of oxygen partial pressures. It was found that the results were consistent with a defect model involving doubly ionized oxygen vacancies arising from both nonstoichiometry and lower valent cation impurities (e.g., Ca('+2)). A method of analysis was also developed to determine the equivalent amount of M('+2) impurities. It was found that the effect of lower valent cation impurities can be compensated by counterdoping with Ta(,2)O(,5). The completely compensated specimen exhibits the predicted behavior of pure ceria. The partial molal enthalpy change, (DELTA)(')H(,O(,2)), of CeO(,2) was calculated from the temperature variation of the electrical conductivity with the counterdoped specimen. The value of (DELTA)(')H(,O(,2)) thus obtained, 9.96 (+OR-) .65 eV, is in good agreement with previously reported results. The electrical conductivity of Ce(,.9)Zr(,.1)O(,2-x) was also measured in the temperature range 800(DEGREES) - 1000(DEGREES)C and 1-10('-3) atm of oxygen pressures. It was found, again, that the results were consistent with a defect model involving doubly ionized oxygen vacancies arising from both lower valent cation impurities and nonstoichiometry. The effect of lower valent cation impurities was also completely compensated by counterdoping with Ta(,2)O(,5). When samples are over-counterdoped or under-counterdoped, the variation of the conductivity dependence upon P(,O(,2)) with varying amounts of Ta(,2)O(,5) is consistent with what is expected based on the law of mass action. Thus, the law of mass action is applicable to Ce(,.9)Zr(,.1)O(,2-x) in the near-stoichiometric region studied. The value of (DELTA)(')H(,O(,2)) was calculated, similarly to the case of "pure" CeO(,2), to be 6.32 (+OR-) .13 eV.
Recommended Citation
CHANG, EDWARD KWA-CHI, "THE IMPURITY EFFECTS AND THE NONSTOICHIOMETRIC DEFECT CHARACTERIZATION OF CERIUM OXIDE(2-X) AND CERIUM(.9)ZIRCONIUM(.1)OXIDE(2-X) IN THE NEAR-STOICHIOMETRIC COMPOSITION RANGE" (1984). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. AAI8502597.
https://epublications.marquette.edu/dissertations/AAI8502597