Nuclear techniques such as perturbed angular correlation (PAC) sample the hyperfine interactions of a large number of probe atoms in specific crystallographic sites. Real crystals contain static defects producing a distribution of electric field gradients (EFGs) that add to the ideal EFG of the crystal at any given probe site. Also, dynamic defects like moving vacancies and interstitial atoms can be present in the crystal and contribute to the distribution of EFGs. The distribution of EFGs leads to line broadening and a change in the observed asymmetry parameter η since the total EFG no longer has the symmetry of the perfect crystal. When both defects are present in a material, obtaining quantitative information from the analysis of PAC spectra is usually very difficult since great care has to be taken to ensure that the source of line broadening is identified correctly. In order to relate the relationship between the static line broadening and changes in the asymmetry parameter η, a uniform random distribution of point charges was used to simulate the static defect EFG. PAC spectra collected on cubic niobium metal, cubic stabilized zirconia and Nb-doped tetragonal zirconia were fitted with this model. Although the quality of the fits is good, more work is needed to clarify the relationship between the new model parameters and the line broadening and asymmetry parameter derived from conventional model fits. The PAC spectra of Nb-doped tetragonal zirconia were fitted with a conventional static model to establish a reliable relationship between line broadening and the asymmetry parameter when only static defects are present in a sample. To account for effects of dynamic defects, a four state stochastic model for vacancy motion was adapted in order to include the line broadening and changes in the asymmetry produced by static defects. As a result, the activation energies corresponding to the rates at which a oxygen vacancy is trapped by, detraps from, and hops among equivalent sites about a PAC probe atom were calculated. The values that were found are physically reasonable, indicating that the dynamics of an oxygen vacancy around a PAC probe atom are satisfactorily described. / Graduation date: 2003

Background: Ceramics have long been amongst the most biocompatible materials known but their mechanical properties have limited their use. During the past few decades zirconia has aroused particular interest as a biomaterial because of its greater flexural strength, fracture resistance and toughness compared to other bioceramics. Technological inventions and developments have made the processing of zirconia-based ceramics possible and thus also the successful processing of dental restorations constructed from this type of material. The properties of zirconia-based ceramics can, however, be affected by, for example, shape, composition, manufacturing processes and subsequent handling. It was, therefore, of particular interest to study in what way recently introduced zirconia-based ceramics intended for odontological applications could be affected by the shape, manufacturing process, composition, grinding and veneering. Methods: By means of newly invented and developed CAM-Software systems with improvements in grinding technology and strategy and hardware technology, cores for single crowns, fixed partial denture (FPD) frameworks and implant-supported abutments and copies were manufactured from a hot isostatic-pressed (HIPed) yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic. In addition, zirconia-based ceramics intended for odontological applications but made from other compositions and/or using different manufacturing techniques were studied. The effects were determined of shape, composition, manufacturing process, heat treatment and veneering of the cores/frameworks on the fracture or bending resistance of various types of ceramic single crowns, FPD frameworks and implant-supported abutments and copies. Results: Different thicknesses in different parts of HIPed Y-TZP cores improved the fracture resistance compared with cores of a uniform thickness resulting in a thicker veneer layer. Machining, heat treatment and veneering affected the fracture resistance of the zirconia-based ceramics studied. In addition, the quality of sintering and composition and type of veneering porcelain used influenced the fracture resistance of zirconia-based ceramics. Conclusion: The results obtained indicate that zirconia-based ceramics have the potential for use as a material in odontological applications. The mechanical properties of zirconia ceramics are, however, affected by, among other things, the shape, composition, manufacturing processes and subsequent handling of the material. These findings have to be taken in consideration in the production processes of zirconia-based ceramic restorations. To further improve their function more studies are needed to elucidate the effects of various manufacturing and handling techniques on the properties of zirconia-based ceramics.

Do ceramics have to be static? This was the question that spurred me into this work, and what kept me working on to achieve the possibility of motion in my ceramic objects. By combining the knowledge gained through my former education as an avionics technician with my interest in the ancient ceramic craft, I strive to create kinetic ceramic handicraft suitable for interaction with an audience. By a series of different phases I slowly go from understanding what kind of motion I want my objects to have, to actually realizing this motion in three-dimensional objects. Through the use of simple models made from corrugated fiberboard followed by more advanced plaster models, combined with different complementary materials such as bicycle inner-tubing and recycled aluminium cans among many others, I, through a vast series of testing, slowly build up a knowledge base later applied to the ceramic objects. The result is for me a success; I have found a way for me to combine ceramics with mechanics. Through this I have created kinetic ceramic handicraft intended for interaction with an audience.

The aim of this work was to contribute to a better understanding of the characteristics and applications of (Ba,Sr)Sm2Ti4O12 microwave dielectric ceramics. The major contents are as follows. Firstly, to establish the correct reaction sequence of (Ba,Sr)Sm2Ti4O12, phases present in different calcining temperatures are identified by X-ray diffraction patterns. When different calcining temperatures are used, the source materials BaO (BaCO3), TiO2 and Sm2O3 are consumed at different calcining temperatures; the intermediate phases BaTiO3, BaTi4O9, and Sm2Ti2O7 reveals and consume at different calcining temperatures before the BaSm2Ti4O12 phase starts to reveal. However, the real solid reaction processes are usually more complex, and some intermediate reaction processes might happen. Secondly, in the (Ba1-xSrx)Sm2Ti4O12 system, SrO can be used to substitute the BaO site and improve the microwave dielectric characteristics. In this study, we find that SrO content in the range of 2 ~ 6 mol% is the acceptable composition because of the higher Q*f values and acceptable and values. Thirdly, the CaO-BaO- Li2O-Sm2O3-TiO2(CBLST) ceramics system was studied. In general, a dielectric material with a high has a large . To adjust to close 0ppm/oC, two or more compounds having negative and positive values are employed to form a solid solution or mixed phases in order to obtain the desired dielectric properties. In this study, BaO was used to substitute the CaO site and improved the microwave dielectric characteristics. Finally, the (Ba0.98Sr0.02)Sm2Ti4O12 system was adopted as a case of applications in dielectric resonator antenna. It possessed a low value of -5.96ppm/¢XC, a high value of 79, and a high Q*f value of 7920 GHz (at 3.311GHz). With the loading of a (Ba0.98Sr0.02)Sm2Ti4O12 dielectric resonator (DR), a circular polarization (CP) design of DR antenna through a cross slot of unequal slot lengths in the ground plane of a microstrip line is fabricated. From the results obtained, it is also found that the present proposed CP design has relatively relaxed manufacturing tolerances, as compared to the conventional CP designs that require slight geometrical modifications of the microstrip patch or DR elements. With the loading of a (Ba0.98Sr0.02)Sm2Ti4O12 superstrate layer and a 1W chip resistor, a compact rectangular microstrip antenna with enhanced gain and wider bandwidth can be implemented. The antenna size is reduced to be ~ 6.05% times of a conventional patch antenna, the proposed structure can have an operating bandwidth of more than six times that of a conventional patch antenna, with an almost equal antenna gain level.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Accompanied by CD-ROM of data and programs used in analyses. Includes bibliographical references (leaves [437]-474).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 286-298). Available also in a digital version from Dissertation Abstracts.

Petrographic and Type:variety analyses of Colha ceramics are used to investigate changes in ceramic production technology and organization during the Early and Middle Postclassic. Postclassic sherds from Colha are grouped by petrofabric, surface treatment, and modes. This dissertation focuses on the petrofabric analysis of the ceramic sherds. The groupings are then compared to locally available raw materials. Changes in technological homogeneity, production specialization, and origin will be examined and related to the general economy of Postclassic Colha. / text

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Grinding/polishing and indentation induced residual stresses were measured by confocal Cr³⁺ fluorescence microscopy with high spatial resolution (~2 μm),obtaining local stress variation information rather than the mean stress averaged over a large sampling volume as is measured by other techniques. Due to the translucency of alumina materials, a substantial portion of the fluorescence signal comes from beneath the surface of the specimen. A probe response function (PRF) was developed taking account of microscope resolution, refraction, absorption and scattering, to quantitatively describe where the collected signal came from. It described the fluorescence intensity variations against defocus distance very well for a range of materials including sapphire, ruby, polycrystalline alumina and AI₂O₃/SiC nanocomposites. Large variations in the residual stresses on ground and polished surfaces were observed, owing to the surface fracture and pullouts. The broad peaks and narrow peaks separated from the spectra collected near the ground/polished surfaces physically represented the two distinct regions in the ground region: a plastically deformed surface layer and the elastically deformed material underneath. A model for the residual stress field taking into account the pullout was proposed using an array of virtual dislocations. The model agreed with the experimental results well when the PRF was included. Tensile stresses were detected on the ground surfaces of polycrystalline aluminas and 2 vol.% SiC nanocomposite, but not on the polished surfaces of polycrystalline aluminas or ground surfaces of 5 and 10 vol.% SiC nanocomposites. This was explained in terms of difference in the amount of pullouts on the surfaces. The depth of deformation was deeper in the ground polycrystalline alumina compared to the polished condition; the depth of deformation in alumina and the AI₂O>sub>3</sub>/SiC nanocomposites were similar (~1 μm) while the compressive stresses in the nanocomposites were greater owing to the reduction in pullout. The main difference between ground alumina and AI₂O₃/SiC nanocomposites was the brittle fracture behavior rather than the plastic deformation. Line scans and area mapping were carried out on 1 kg loaded Vickers indentations of alumina-based ceramics. Tensile stresses were found at the tips of radial cracks and lateral cracks and compressive stresses were found around the indent impression. The line scan results in the elastic regions agreed qualitatively with Yoffe's model and the quantitative discrepancy was attributed mainly to the cracking that relaxed the stresses. The differences in residual stresses between alumina and AI₂O₃/SiC nanocomposites were small if measured with high spatial resolution but it would be exaggerated with lower resolution.

published_or_final_version / Architecture / Master / Master of Architecture