Date of Award
8-1981
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical Engineering
First Advisor
Robert N. Blumenthal
Second Advisor
Robert F. Brebrick
Third Advisor
Raymond A. Fournelle
Fourth Advisor
Walter M. Hirthe
Fifth Advisor
Martin A. Seitz
Abstract
The method of incorporation of the relatively small Ar+4 dopant cation was infered from pycnometirc density measurements. Up to, at least, 14 m/o ZrO2 the Zr+4 ions occupy normal Ce+4 sites.
The electrical conductivity of ZrO2-doped CeO2was measured in pure oxygen in the range 600° - 1300°C for ZrO2 compositions up to 18 m/o. Where comparisons could be made with the work of other investigators the agreement was excellent; any deviation at all being shown to be due to the greater purity of the starting materials used in this study.
The electrical conductivity, σ, and the deviation from stoichiometry, x, of 10 m/o ZrO2-doped CeO2 has been measured in the range 800° - 1300°C for PO2's between 1 and 10-23 atms. The quantity ΔHO2 determined from the thermogravimetric data showed that at small x (log x ≈ -2.25) the energy to form a defect in 10 m/o ZrO2-doped CeO2 was only 7.3 ev, while for "pure" CeO2, that energy is ~9.8 ev. This decrease in defect formation energy is consistant with the higher conductivity and greater deviation from stoichiometry observed in 10 m/o ZrO2-doped CeO2 at high PO2.
The temperature dependence of electrical conductivity at constant nonstoichiometric composition was obtained by combining the equilibrium data. For each composition a high temperature and low temperature region was observed. The activation energy for electron motion calculated from the low temperature slopes was greater than that for "pure" CeO2 while that calculated from the high temperature slopes was more consistant with that for "pure" CeO2.
The temperature dependence of electrical conductivity at constant nonstoichiometric compositions was also measured by a non-equilibrium technique. This data was represented by a single activation energy over the entire temperature range and its magnitude and compositional dependence between that calculated from the high temperature and low temperature slopes of the combined analysis.
The controversy over the proper nobility model to be used for a description of electron hopping is addressed. It is shown that it is not currently possible to determine the proper nobility model from an analysis of the temperature variation of electrical conductivity at constant nonstoichiometric composition.