The properties of superconducting YBa₂Cu₃O₇₋(δ) thin films have been studied. Films have been prepared by multilayer deposition followed by ex situ furnace annealing. Deposition consists of a combination of dc triode sputtering from metallic targets of Y and Cu and thermal evaporation from a BaF₂ source. Superconducting and structural properties of the films strongly depend on the annealing conditions. Several heat treatment cycles were investigated, as well as different compositions. Best results were obtained for films deposited on (100) SrTiO₃ substrates, exhibiting T(c)(onset) as high as 92 K and zero resistance by 85 K. The second part of this dissertation examines the properties of ceramic Nd₂₋ₓCeₓCuO₄₋(δ) and Nd₁ͺ₈₅Ce₀ͺ₁₅(Cu₁₋(y)Zn(y))O₄₋(δ) bulk samples. Superconducting properties are examined as a function of x and y. Accurate (± 0.001 Å) lattice parameter calculations are performed from experimental x-ray diffraction data. Comparisons with previous zinc-doping studies in the hole superconducting material La₁ͺ₈₅Sr₀ͺ₁₅CuO₄₋(δ) are made. Theoretical implications and the question of electron-hole symmetry in the copper oxide superconductors are also discussed.

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Abstract The proposed research of investigating the interaction between high-temperature superconductors and linear motors is introduced. Background on levitated transportation, high-temperature superconductor applications and supercon- ductor theory is given. An analytical model is developed for calculating thrust and levitation forces produced by 3-phase windings on a pair bulk high- temperature superconductors. Results produced by this model for a spacing of 1 pole-pitch and 1 2 pole-pitch are presented. In order to verify the analytical model a prototype system is built from a linear motor primary and vehicles containing 2 rows of superconductors. Two vehicles are built with different spacing between the rows of superconductors in order to investigate the ef- fect of their positioning, with respect to the pole-pitch, on the thrust forces produced. Measured forces on these two vehicles are then compared with pre- dicted values showing that the model predicts the forces with less than 5% error. Problems with the analytical model are also discussed. Finally it is con- cluded that the model developed provides insight to the relationship between high-temperature superconductors and travelling magnetic waves, and that a 1 pole-pitch separation between superconductors produces higher forces. Rec- ommendations for further development of the prototype system are also given.

by Siu Wing Hon. / On t.p. T"c", "2", "3", and "7-x" are subscripts following "superconducting" in the title. / Parallel title in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves [79]-[80]). / Acknowledgement --- p.i / Abstract --- p.ii / Table of Content --- p.iii / Chapter Chapter 1 : --- Introduction / Chapter Chapter 2 : --- Growth of YBCO on Spinel / Chapter 2-1. --- Why Spinel --- p.2-1 / Chapter 2-2. --- Film Deposition Technique --- p.2-3 / Chapter 2-2.1 --- Magnetron Sputtering Technique --- p.2-3 / Chapter 2-2.2 --- Pulsed Laser Ablation --- p.2-4 / Chapter Chapter 3 : --- Composition Analysis by XRF / Chapter 3-1. --- Introduction --- p.3-1 / Chapter 3-2. --- Minimum Penetration Depth of EDX for YBCO film --- p.3-5 / Chapter 3-3. --- Thin Film Method and Thin Film Limit --- p.3-9 / Chapter 3-4. --- XRF Setup --- p.3-14 / Chapter 3-5. --- Calibration --- p.3-14 / Chapter 3-5.1 --- Chemical method --- p.3-18 / Chapter 3-5.2 --- Absorption Factor --- p.3-18 / Chapter 3-5.3 --- Diffusion Rate --- p.3-22 / Chapter 3-5.4 --- Justification of Thin Film Method --- p.3-22 / Chapter 3-5.5 --- Result of Calibration by Chemical Method --- p.3-24 / Chapter 3-5.6 --- Calibration by Rutherford Backscattering --- p.3-28 / Chapter 3-6. --- Discussion on XRF --- p.3-31 / Chapter 3-6.1 --- Effect of diffraction line by substrate on X-ray spectrum --- p.3-31 / Chapter 3-6.2 --- Stability of X-ray power supply and its influence on spectrum --- p.3-34 / Chapter Chapter 4 : --- Structural Analysis and Rapid Thermal Annealing / Chapter 4-1. --- XRD Setup --- p.4-1 / Chapter 4-2. --- XRD Analysis --- p.4-2 / Chapter 4-2.1 --- θ-2θ Scan --- p.4-1 / Chapter 4-2.2 --- Phi Scan --- p.4-3 / Chapter 4-2.3 --- Study of Diffraction Peak --- p.4-9 / Chapter 4-3. --- RTA and its influence on structure --- p.4-11 / Chapter 4-3.1 --- RTA Setup --- p.4-13 / Chapter 4-3.2 --- Structural Improvement by RTA --- p.4-13 / Chapter Chapter 5 : --- Conclusion --- p.5-1 / Chapter Appendix : A. --- Mathematical Derivation of Thin Film Limit / Chapter B. --- Powder Diffraction Patterns of YBCO system / Reference

Ling Siu-hing. / Title also in Chinese characters. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 220-227). / ACKNOWLEDGEMENT --- p.i / ABSTRACT --- p.ii / Chapter Chapter 1 --- Ceramic thin film --- p.1 / Chapter 1. 1 --- """New stone era""---the importance of ceramics" --- p.1 / Chapter 1.2 --- The importance of epitaxial growth of YBCO films --- p.4 / Chapter 1.3 --- The importance of epitaxial growth of PZT films --- p.9 / Chapter 1.4 --- The similar structures of YBCO and PZT --- p.10 / Chapter Chapter 2 --- Epitaxy --- p.12 / Chapter 2. 1 --- Introduction --- p.12 / Chapter 2.2 --- Basic principle --- p.13 / Chapter Chapter 3 --- Sample preparation Techniques --- p.25 / Chapter 3.1 --- A glimpse at epitaxial film deposition --- p.25 / Chapter 3.2 --- Magnetron sputtering --- p.28 / Chapter 3.2.1 --- Principle --- p.28 / Chapter 3.2.2 --- Set-ups --- p.30 / Chapter 3.2.3 --- High pressure magnetron sputter gun --- p.33 / Chapter 3.2.4 --- Type II unbalanced magnetron gun modification --- p.42 / Chapter 3.3 --- Pulsed Laser Deposition (PLD) --- p.54 / Chapter 3.4 --- Rapid thermal annealing (RTA) --- p.62 / Chapter Chapter 4 --- Characterizations-principles and setups --- p.66 / Chapter 4.1 --- Structure-X-ray diffractometer --- p.66 / Chapter 4.1.1 --- Setup --- p.57 / Chapter 4.1.2 --- Characterization --- p.71 / Chapter 4.1.3 --- High temperature X-ray diffractometer (HTXRD) --- p.83 / Chapter 4.2 --- Surface morphology --- p.86 / Chapter 4.2.1 --- Scanning electron microscopy (SEM) --- p.86 / Chapter 4. 3 --- Composition --- p.89 / Chapter 4.3.1 --- Energy dispersive X-ray spectroscopy --- p.89 / Chapter 4.3.2 --- Rutherford backscattering spectrometry (RBS) --- p.91 / Chapter 4.4 --- Other characterization techniques --- p.93 / Chapter 4.4.1 --- Thickness measurement --- p.93 / Chapter 4.4.2 --- Measurement of Tc in YBCO --- p.93 / Chapter 4.4.3 --- Thermomechanical analysis system (TMS) --- p.95 / Chapter 4.4.4 --- Differential scanning calorimeter (DSC) --- p.98 / Chapter Chapter 5 --- Epitaxial films --- p.99 / Chapter 5. 1 --- YBCO films --- p.99 / Chapter 5.1.1 --- YBCO on sapphire --- p.99 / Chapter 5.1.2 --- YBCO on spinel (MgAl2O4) --- p.115 / Chapter 5.1.3 --- YBC0//SrTi〇3//spinel --- p.130 / Chapter 5.1.4. --- YBCO on Mg〇 --- p.134 / Chapter 5.1.5 --- YBCO on SrTi〇3(110) --- p.143 / Chapter 5.2 --- PZT films --- p.182 / Chapter 5.2.1 --- PZT on MgO --- p.182 / Chapter 5.2.2 --- PZT on spinel --- p.188 / Chapter 5.2.3 --- High temperature structural transition of PZT films --- p.195 / Chapter Chapter 6 --- Conclusion --- p.218 / REFERENCES --- p.220

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

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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.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.