A thermodynamic study of nonstoichiometric cerium dioxide |
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Authors: | R.J. Panlener R.N. Blumenthal J.E. Garnier |
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Affiliation: | Metallurgy and Materials Science, College of Engineering Marquette University, Milwaukee, WI 53233, U.S.A. |
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Abstract: | Thermogravimetric measurements were performed on nonstoichiometric CeO2?x in the temperature range 750–1500°C and from oxygen pressures of 10?2 to 10?26 atm. From this data the deviation from stoichiometry x = x(T, Po2) was determined. The thermodynamic quantities Δo2 and Δo2 were calculated in the region 0.001? x ? 0.3 and found to be independent of temperature.In the composition region 0.001< x < 0.006, the variation of Δo2 with x is consistent with a defect model involving randomly distributed doubly ionized oxygen vacancies. The experimental dependence of x and σ (electrical conductivity) is shown to be consistent with this model as Δo2 (≈ -10 eV) exhibits a slight dependence on x. It is postulated that the variation in Δo2 may result from lattice parameter increases with x, while the defects remain essentially randomly distributed.In the composition region 0.006 < x < 0.1, x ∝ with 1 < n < 5, and in the region 0.1 < x < 0.3, x ∝ with n increasing rapidly with x to n? 30. This behavior is believed to result from increasing defect interaction with increasing departures from stoichiometry. It is interesting to note that the ordered phase observed by Bevan and Kordis between CeO1·72 and CeO1·70 was not observed in this study at temperatures between 1300° and 1500°C. |
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