The problem of aftereffects in perturbed angular correlation studies of ceria Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/qz20sw83z

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  • Perturbed Angular Correlations (PAC) spectroscopy is an effective local probe technique often employed in the characterization of defects or phase transitions in any of a variety of materials. This technique relies upon the ability of probe nuclei to function as gauges of the magnetic fields and electric field gradients local to the probes once they have been introduced (doped) into the lattice in question. It has been seen that disturbances in the electronic environment of the probe nucleus due to, for instance, the presence and movement of electron holes can impair the ability of the probe to function, thereby undermining the efficacy of the approach. This impairment and subsequent distortion of lattice information provided are known as the problem of "aftereffects." In PAC studies of ceria, a poor conductor, disturbances in the electronic environment of the ¹¹¹Cd probe subsequent to electron capture result in bothersome aftereffects in the PAC data spectrum. These aftereffects are believed to be characterizable in terms of two rates: electronic hole hopping and escape. A model that treats the aftereffect in terms of the hopping and escape rates associated with one electronic hole (and which assumes the system is otherwise unperturbed) was tested for · low temperatures (10 K). The data indicate that this aftereffect model as it stands does not describe the behaviour of the system at low temperatures. However, it is clear that the aftereffect problem is exacerbated by low temperatures, though the increase of the fraction of aftereffected sites is not smooth over the temperature range 10-293 K. The problem of aftereffects is pronounced in 0.1% Nb-doped ceria. Typically, room temperature measurements of this system show greater than 70% aftereffected sites. No aftereffect whatsoever was found in 1% In-doped ceria at room temperature.
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  • File scanned at 300 ppi (Monochrome, 256 Grayscale) using Capture Perfect 3.0 on a Canon DR-9050C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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