Date of Award

Fall 1980

Document Type

Dissertation - Restricted

Degree Name

Doctor of Philosophy (PhD)



First Advisor

Blumenthal, Robert N.

Second Advisor

Hirthe, Walter


A unique, highly sensitive capacitance manometer system useful for determining the deviation from stoichiometry in metal oxides as a function of oxygen partial pressure has been constructed, evaluated, and used to determine the oxygen partial pressure dependence of the deviation from stoichiometry in nonstoichiometric cerium dioxide at 800°C. The range of partial pressures covered in this study was from 10-12 atm. to 10-17 atm. For values of log x (in Ceo2_x) between -2.4 and -3.0 obtained in this study was virtually identical to that obtained by Panlener who used a microbalance to determine the dependence of x upon PO2. In this region the x-dependence upon PO2 was found to be approximately -1/5. For values of x less than 0.001 the data obtained in this study showed significantly less scatter than that obtained by other investigators using a microbalance. Because of this, and because it was shown that "formula" (the uncertainty in x) could be expressed as "formula", it was concluded that a capacitance manometer system can measure x more reliably in this range than a microbalance can. In addition to exhibiting less scatter in this range, the data obtained in this study began to deviate significantly from the existing data as smaller values of x were approached. The dependence of x upon PO2 also changed in this reason. Rather than remaining at -1/5, it became more complicated and appeared to be approaching -1/4. This more complicated dependence of x upon P02 suggested that, for log x less than -3.0, the behavior of nonstoichiometric cerium dioxide was influenced by the presence of small amounts of impurities. In order to analyze the data in this range a theoretical study of the partial pressure dependence of the deviation from stoichiometry in the presence of M+ 2 type impurities was performed. The results of this study showed that the observed partial pressure dependence of the deviation from stoichiometry in ceria was consistent with a model involving randomly distributed doubly ionized oxygen vacancies along with localized electrons and small amounts of calcia impurities...



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