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Thesis (Ph. D.)--California Institute of Technology, 1992. UM #92-32, 184. / Advisor names found in the Acknowledgments pages of the thesis. Title from home page. Viewed 02/01/2010. Includes bibliographical references.

Apparatus to measure the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) at temperatures between 20K and 120K has been designed and constructed. The thermal conductivity is measured using a longitudinal steady state heat flow technique. Thermal conductivity measurements have been performed upon a sample of YBa(_2)Cu(_3)O(_7-δ) which has been subjected to a series of heat treatments in order to remove oxygen from the material. The measurements show conclusively that the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) is very strongly influenced by the oxygen content of the material. A reduction of the oxygen content of the material results in a substantial lowering of the thermal conductivity. To explain this result, a quantitative model has been constructed; the model demonstrates that consideration of the changes in phonon interactions alone cannot account for the differences in the behaviour of the thermal conductivity of YBa(_2)Cu(_3)O(_6) and YBa(_2)Cu(_3)O(_7). In addition; the model, shows that there must be a significant carrier contribution to the thermal conductivity in both the normal and superconducting states. A physical process has been proposed which provides the required large carrier contribution below T(_c). Further studies have been performed on a series of samples of YBa(_2)Cu(_3)O(_7-δ) which were sintered at slightly different temperatures. Qualitative analysis of the physical properties, of these samples has been performed.

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

Methods of processing large grained textured superconductor have been successfully developed, based on a melt texturing process. Large grained textured superconductor with grain size over 10mm along the growth direction and Jc over 3600A/cm² (77K, 0.5 Tesla) has been produced in both one - zone and two - zone furnaces with good reproducibility. Two kinds of design of reactive metal contacts have been proposed and investigated, aiming to make low resistivity contacts with strong mechanical strength. Three possible reactive contact metals have been tested for contact making, and the microstructures at the interfaces have been studied to find the relations between contact resistivity and contact processing conditions. Titanium/noble metal multilayer contacts is a promising type of contact technique for low resistivity and strong mechanical bonds. Gold and silver contacts give resistivities among the best reported results in the literature, and they turned out to be extremely stable in time, could withstand repeated thermal cycling from room temperature to 10K and yield very reproducible R-T curves. The electrochemical titration method has been used to increase the oxygen stoichiometry of bulk textured YBa₂Cu₃O_7-x samples. The electrochemical titration method can further oxidize melt textured thick film YBa₂Cu₃O_7-x samples in which it may be difficult to further improve oxygen content by conventional annealing. The solid state electrochemical cell has been used to study the thermodynamic properties of the Y-Ba-Cu-O system at high oxygen pressure by measuring the oxygen activity versus time continuously immediately after the electrochemical titration. A series of computer models have been set up according to the microstructure of the contact interface to simulate the complicated contact resistivity behaviours. The nature of, and geometry of, the reaction products at the contact interfaces may be revealed by the temperature dependence of the contact resistance. This information combined with direct observations on the structure and chemistry of the contacts provided a fuller understanding of conduction mechanism at the contact interface.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (leaves l05-110). Also available via World Wide Web.

by Yu-Kit Lam =鉍系超導體在各製備階段之機械及超導特性 / 林宇傑. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Yu-Kit Lam = Bi xi chao dao ti zai ge zhi bei jie duan zhi ji xie ji chao dao te xing / Lin Yujie. / Table of Contents --- p.i / Acknowledgments --- p.iv / Abstract --- p.v / Chapter Chapter 1 --- Related Work on Bulk Bi-based High Tc Superconductor --- p.1 / Chapter 1.1 --- Historical Background of Superconductivity --- p.1 / Chapter 1.2 --- Basic Properties of Superconductivity --- p.4 / Chapter 1.3 --- Basic Properties of Bi-based Superconductor --- p.7 / Chapter 1.4 --- Fabrication Methods of Bi-based Superconductor --- p.12 / Chapter 1.4.1 --- Precursor Preparation --- p.12 / Chapter 1.4.1.1 --- Solid State Reaction Method --- p.12 / Chapter 1.4.1.2 --- Sol-gel Method --- p.15 / Chapter 1.4.1.3 --- Co-decomposition Method --- p.17 / Chapter 1.4.1.4 --- Freeze-drying and Spray-drying Methods --- p.17 / Chapter 1.4.1.5 --- Comparison for precursor preparation methods --- p.18 / Chapter 1.4.2 --- Pelletization and Sintering --- p.20 / Chapter 1.5 --- Potential applications of Bi-based superconductors --- p.22 / Chapter 1.5.1 --- Criteria for practical applications --- p.22 / Chapter 1.5.2 --- Superconducting tapes --- p.23 / Chapter 1.5.3 --- Current leads --- p.26 / Chapter 1.6 --- Objectives of the Project --- p.27 / Chapter 1.7 --- References --- p.28 / Chapter Chapter 2 --- Fabrication of Bulk Bi(Pb)-2223 Superconductor --- p.33 / Chapter 2.1 --- Introduction --- p.33 / Chapter 2.2 --- Precursor Preparation --- p.33 / Chapter 2.3 --- Grinding Process --- p.34 / Chapter 2.4 --- Pelletization Process --- p.35 / Chapter 2.5 --- The Sintering --- p.37 / Chapter 2.6 --- Characterizations --- p.38 / Chapter 2.7 --- References --- p.40 / Chapter Chapter 3 --- Principles and Instruments of Characterizations --- p.41 / Chapter 3.1 --- Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy --- p.41 / Chapter 3.1.1 --- Basic Principle --- p.41 / Chapter 3.1.2 --- Sample Preparation --- p.42 / Chapter 3.2 --- Crystal Structure Determination Using X-ray Diffraction Spectroscopy --- p.44 / Chapter 3.3 --- Vibrating Sample Magnetometer --- p.48 / Chapter 3.3.1 --- Basic Principle --- p.48 / Chapter 3.3.2 --- Sample Preparation --- p.49 / Chapter 3.4 --- Standard Four-Probe Method for Electrical Measurement --- p.51 / Chapter 3.5 --- Density Measurement of Sintered Samples --- p.52 / Chapter 3.6 --- Hardness Tests --- p.54 / Chapter 3.7 --- Determination of Flexural Strength of Sintered Samples --- p.56 / Chapter 3.8 --- References --- p.57 / Chapter Chapter 4 --- Results and Discussions / Chapter 4.1 --- Results from X-Ray Diffraction Spectroscopy --- p.58 / Chapter 4.1.1 --- Green Pellet --- p.58 / Chapter 4.1.2 --- 50-Hour Sintered Pellet --- p.58 / Chapter 4.1.3 --- "100-Hour, 150-Hour, and 200-Hour Sintered Pellets" --- p.59 / Chapter 4.1.4 --- Volume Fraction of the High Tc Phase --- p.59 / Chapter 4.2 --- Microstructure Observed by Scanning Electron Microscopy --- p.63 / Chapter 4.2.1 --- Green Pellet --- p.63 / Chapter 4.2.2 --- 50-Hour Sintered Pellet --- p.64 / Chapter 4.2.3 --- "100-Hour, 150-Hour, and 200-Hour Sintered Pellets" --- p.64 / Chapter 4.3 --- Chemical Composition Using Energy Dispersive X-ray Spectroscopy --- p.68 / Chapter 4.4 --- Results from Vibrating Sample Magnetometer --- p.71 / Chapter 4.5 --- Densification of Sintered Samples --- p.75 / Chapter 4.6 --- Hardness at Various Stages of Processing --- p.77 / Chapter 4.7 --- Flexural Strength at Various Stages of Processing --- p.79 / Chapter 4.8 --- I-V Characterization Using Standard Four-Probe Method --- p.82 / Chapter 4.9 --- Weibull Modulii of Sintered Samples --- p.85 / Chapter 4.10 --- Future Oultlook --- p.86 / Chapter 4.11 --- References --- p.87 / Chapter Chapter 5 --- Summary --- p.89 / Appendix A Polishing of Pelletizing Mold / Chapter A.1 --- Introduction --- p.92 / Chapter A.2 --- Grinding Process --- p.92 / Chapter A.3 --- Final Polishing Process --- p.93

Zhao Kun. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese. / Zhao Kun.

In this thesis, we study the effects of doping in two-dimensional quantum antiferromagnets. We consider cases where the undoped parent compound is a Mott insulator with long-range antiferromagnetic order and focus on the low-doping situations. The limit of localized impurities is studied in a system consisting of a host magnet and two additional weakly coupled spins. We derive the effective Hamiltonian describing the interaction between these impurities as a function of their distance and show that it exhibits xyz anisotropy, leading to NMR and EPR line broadening. We calculate the magnetization disturbance in the host magnet induced by a single impurity and find that it always enhances Neel order. Relaxing the localization constraint, we investigate the single-hole dynamics of the t-J model on the honeycomb lattice. Using exact diagonalizations, series expansion and the self-consistent Born approximation, we calculate the quasi-particle dispersion, bandwidth and residues and compare our findings with the well-established results for the square lattice. Similar to the latter case, we find an almost flat band along the edges of the magnetic Brillouin zone and well-defined hole pockets around the corners. The most important part of this thesis is devoted to the magnetic properties of lightly doped La2-xSrxCuO4, the simplest and by far most studied cuprate superconductor. Starting from the undoped parent compound, we calculate the spin-wave spectrum and the spin-flop transitions in a uniform magnetic field at zero temperature. We then consider the low-doping regime and derive the effective field theory describing the spin dynamics in insulating La2-xSrxCuO4, x ≤ 0.055, at low temperature. The spin structure resulting from the spiral solution of the extended t-J model, obtained by taking into account the Coulomb trapping of holes by Sr ions, is confined in the copper-oxide planes. Our solution explains why the incommensurate structure is directed along the orthorhombic b axis and allows us to calculate the positions and shapes of the neutron scattering peaks numerically. These results are in perfect agreement with experimental data. We also show that topological defects (spin vortex-antivortex pairs) are an intrinsic property of the spin-glass ground state.