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A microscopic study of the interaction between aliovalent dopants and native defects in group IV oxides : indium and cadmium in ceria and zirconia

In order to understand better the defect structure and dynamics associated
with lower valent dopants complexed with native defects in group IV oxides, In/Cd
perturbed angular correlation spectroscopy was performed in ceria and zirconia. Examining
the orientation symmetry axis of defects in ceria single crystals at low temperature
has allowed the identification of a cadmium with a bound near-neighbor
oxygen-vacancy complex as well as a complex involving a cadmium with two opposing,
near-neighbor oxygen vacancies. The orientation of the symmetry axis of a third
complex is reported; however, this information is not sufficient to identify it. Complementing
these low temperature studies, the dynamics of the cadmium/oxygen-vacancy
interaction in zirconia at high temperatures was studied. The motion of the oxygen
vacancy at high temperatures results in a damping of the PAC signal. This damping
is not well characterized by the heuristic Marshall-Meares PAC fitting function, and
a model is proposed to fit the data in terms of three physical parameters associated
with the vacancy's motion. These parameters are the rate at which a bound oxygen
vacancy hops among equivalent sites about the probe, the rate at which a bound
vacancy detraps, and the rate at which a vacancy is trapped by cadmium. Fits of
individual spectra using this model give respective activation energies of 0.3-0.6 eV,
0.9-1.6 eV, and 0.4-0.6 eV. The uncertainty in these energies can most likely be
reduced by fitting spectra from multiple temperatures simultaneously. Despite the
large uncertainty in the fitted energies, the values are physically reasonable and indicate
that the model adequately describes the motion of the oxygen vacancy about
cadmium. / Graduation date: 1997

Identiferoai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34309
Date11 March 1997
CreatorsZacate, Matthew O.
ContributorsGardner, John A.
Source SetsOregon State University
Languageen_US
Detected LanguageEnglish
TypeThesis/Dissertation

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