This thesis describes results obtained using high resolution electron microscopy, acoustic microscopy and chemical analysis to study the structure and properties of the superionic β-aluminas. The acoustic microscopy and chemical analysis results relate solely to sodium β- and β -alumina, which are used as the solid state electrolyte in the sodium/sulphur cell. The high resolution electron microscopy results cover sodium β- and β-alumina as well as a number of ion-exchanged β-aluminas. The β-alumina structure consists of spinel-like blocks separated by the so-called conduction planes. The conduction planes have a low density, and contain all the mobile cations. Lattice images of sodium β- and β-alumina, silver β-alumina, ammonium/hydronium β-alumina, gadolinium β -alumina and divalent and trivalent europium β -alumina are presented and discussed. A hitherto unreported long-period structure in sodium β-alumina is shown, as is superlattice ordering in the divalent and trivalent β-aluminas. Defects in these materials are also discussed. The most common damage mode in the β -aluminas, due to electron beam irradiation, is the loss of the mobile-ion containing planes, and the subsequent collapse and shear of the structure to form broad defect spinel blocks. It is shown that collapse vectors determined for sodium β-alumina can also be applied to ammonium/hydronium β-alumina. Two further damage modes observed in this β-alumina are also discussed. A damage mode has been observed in sodium B-alumina and silver β-alumina which involves the extrusion of material to the crystal surface. Electron diffraction patterns from the extruded material have been indexed. The acoustic microscope has been used to examine bulk sodium β/β-alumina electrolyte tube specimens. Images of rectangular features present in the tubes (approximately 40um in length) are presented and the possible nature of the features is discussed.

published_or_final_version / abstract / Physics / Master / Master of Philosophy

Ph.D. / Materials Science and Engineering / Polytitanates in the BaO- TiO2 system with Ba:Ti ratios ranging from 1:2 to 1:5 were prepared using a low temperature technique developed by Pechini. The samples were heated at 600 to 1300°C in oxygen. Room temperature Raman spectroscopy was used to investigate the phase relations in this system. Results of this study indicate the following: except for BaTi4O9, the powders of these compounds were amorphous when heated at 600°C for 4hrs; the compound BaTi2O5 is a low temperature stable phase; Ba6Ti17O40 forms only at temperatures above 1100°C; Ba4Ti13O30 does not form below 1000°C; the single phase BaTi4O9 structure was observed at 1200°C'; the Ba2Ti9O20 phase is obtained only after long heat treatment at 1200°; BaTi5O11 was stable up to 1200°C, at which it decomposes into Ba2Ti4O20 and TiO2. After determination of stability relationships in this system, the electrical conductivities of these compounds were examined as a function of temperature and oxygen partial pressure. For all the temperatures (850-1150°C) studied, the conductivities of these compounds increased with decreasing oxygen partial pressure resulting in n-type properties throughout the whole P[subscript O2] range (10[superscript -19 - 1atm). The P[subscript O2] dependencies of the electrical conductivity were found to be linear for an extensive range of oxygen partial pressures. On the basis of structural considerations the conductivity data was described by a majority defect model consisting of both singly and doubly ionized oxygen vacancies. For lower oxygen partial pressure values a drastic change in the electrical conductivity was observed. This is believed to result from increasing defect interaction for larger departures from stoichiometry. A defect model based on this interaction is proposed to account for the observed sharp change in the electrical conductivity values.

No description available.

No description available.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Previous work has shown that laser-induced desorption (LID) can prove useful for the determination of surface contamination. However, because of the nature of small-spot sampling utilized in the previous work, it proved rather difficult to gather statistically significant data. A solution to this problem that still allowed sampling the surface with small focused laser spots was to automate the sample manipulation, laser control, and data acquisition of the system. With the automation of the LID facility in place, a detailed study of the LID of water/heavy water (H₂O/D₂O) was undertaken. As in the earlier work, samples were irradiated with a hydrogen fluoride/deuterium fluoride (HF/DF) laser beam focused inside an ultrahigh vacuum (UHV) chamber. The molecules desorbed from the sample surface were partially contained in a glass envelope that also contained a quadrupole mass analyzer. Samples consisted of bulk-etched CaF₂ and optical thin-film coatings of CaF₂--undosed or H₂O/D₂O dosed--on a variety of substrates. Some analysis was performed on cleaved, single-crystal alkali halides. The focused laser spot size was 155 μm (l/e² diameter) for the HF laser and 138 μm (l/e² diameter) for the DF laser. Between 400 and 800 sites per sample were tested for each desorption onset analysis. A study was also performed to test the possibility of correlation between (1) laser-induced damage and defects and (2) laser-induced desorption and adsorption sites for some of the samples listed above. Attempts to deuterate and hydrate CaF₂ thin films met with limited success as laser-induced desorption samples. Other analysis techniques showed that dosing during the coating process produced a more ordered coating; in fact, dosing with H₂O reduced the optical absorption in the "H₂O" band, modified the damage morphology, and, along with a low temperature bakeout, raised the laser-damage threshold.

A numerical method is developed to determine the dynamic behavior of delamination and transverse cracks in multilayered plates. The plate is subjected to a time dependent antiplane shear stress field which is acting on the plate surfaces. The interaction of waves diffracted at the crack tip with those reflected at the plate boundaries and transmitted at the material interface makes the problem very complicated, so analytical study of this problem cannot be carried out with our present state of knowledge; hence the problem is solved numerically. The finite element equations are obtained by variational calculus applied in the frequency domain. Thus time intregration schemes are avoided, but time dependent response can still be obtained after inverting the frequency dependent response spectra numerically by Fast Fourier Transform (FFT) routine. Another advantage of the frequency domain analysis is that the resonance frequency can be easily detected from the sharp peaks of the response spectra. The numerical difficulty associated with the singular behavior of the stress field near the crack tip has been avoided by using quarter point elements. The numerical results obtained from this investigation are compared with analytical results to verify the accuracy of the method.

No description available.