Date of Award

Fall 1973

Document Type

Dissertation - Restricted

Degree Name

Doctor of Philosophy (PhD)


Electrical and Computer Engineering

First Advisor

Seitz, Martin A.

Second Advisor

Mueller, M. H.

Third Advisor

Cartz, L.


Polycrystalline samples of Ceo2-x (O < x <0.21) have been examined in the temperature range from 800° to 1000°C using x-ray and neutron diffraction techniques. The atomic defect structure of non-stoichiometric ceria was studied in this temperature range by adjusting the oxygen partial pressure between 1 and 10-21 stomospheres. Over this range of temperature and oxygen partial pressure, it has been observed that the lattice expands as a function of increasing defect concentration and only fluorite-like diffraction peaks have been observed. For the x-ray experiments, the integrated intensities of the Bragg reflections were analyzed for CeO1.91, at 900°C, using difference electron density techniques. It was observed that the cation sublattice is essentially intact and evidence was found that oxygen vacancies are the predominant atomic defects in nonstoichiometric ceria. X-ray least-squares analysis on Ceo2_x' (0 < x < 0.21) from 800° to 1000°c supported these results and also showed that the temperature factors of both cations and anions increase with increasing defect concentration, implying greater mean-squared displacement of the atoms from their equilibrium positions. The neutron experiments were carried out at 900°c for Ce02-x' (0 < x < 0.21), where the Bragg reflections were analyzed in terms of various defect models . For x < 0.11, good agreement (residual < 1.0%) was obtained by assuming a random distribution of defects among available anion sites, in the statistically representative unit cell. The vacancy concentrations determined from the neutron data are consistent with the thermogravimetric determinations. For O < x < 0.11, the temperature factors of both the metal and oxygen atoms increase nth increasing vacancy concentration, implying greater root-mean-square displacement of the atoms from their equilibrium positions. However, for x > 0.11 the analysis of the neutron data indicates a smaller oxygen vibrational amplitude than in the near-stoichiometric compositions, but this is accompanied by a shift in the equilibrium position of the oxygen atom. The effect of anharmonic thermal motion has also been considered, but by itself, cannot explain the neutron data. The results of the present study correlate well with the x-ray studies and may be related qualitatively to thermodynamic behavior of the substoichiometric Ce02-x system.



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