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by Hon Wan Man = 鎂和硼化鎂複合材料的研究 / 韓韻文. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Hon Wan Man = Mei he peng hua mei fu he cai liao de yan jiu / Han Yunwen. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgements --- p.v / Table of contents --- p.vi / List of tables --- p.x / List of figures --- p.xi / Chapter Chapter 1 --- Introduction --- p.1-1 / Chapter 1.1. --- Background --- p.1-1 / Chapter 1.1.1. --- Conventional and unconventional superconducting materials --- p.1-1 / Chapter 1.1.2. --- Type I and type II superconductors --- p.1-2 / Chapter 1.1.3. --- Critical Temperature and Magnetic Properties (M-H Loops) --- p.1-4 / Chapter 1.2. --- Magnesium Diboride MgB2 --- p.1-6 / Chapter 1.2.1. --- Introduction --- p.1-6 / Chapter 1.2.2. --- Potential application and recent work of MgB2 --- p.1-6 / Chapter 1.2.2.1. --- Thin films --- p.1-7 / Chapter 1.2.2.2. --- Wires and tapes --- p.1-8 / Chapter 1.2.2.3. --- Powders and single crystal --- p.1-8 / Chapter 1.2.3. --- Factors affecting critical temperature in MgB2 --- p.1-9 / Chapter 1.2.3.1. --- Critical temperature versus lattice constants --- p.1-9 / Chapter 1.2.3.2. --- Critical temperature versus pressure --- p.1-9 / Chapter 1.3. --- Mg-based metal matrix composites (Mg-MMCs) --- p.1-10 / Chapter 1.4. --- Objectives and approaches --- p.1-11 / Chapter 1.5. --- Thesis layout --- p.1-12 / Chapter 1.6. --- References --- p.1-13 / Figures --- p.1-16 / Tables --- p.1-20 / Chapter Chapter 2 --- Methodology and instrumentation --- p.2-1 / Chapter 2.1. --- Introduction --- p.2-1 / Chapter 2.2. --- Experimental procedures --- p.2-1 / Chapter 2.3. --- Samples fabrication --- p.2-2 / Chapter 2.3.1. --- Powder metallurgy method (P/M) --- p.2-2 / Chapter 2.3.2. --- Argon atmosphere tube furnace heat treatment --- p.2-3 / Chapter 2.4. --- Characterization --- p.2-3 / Chapter 2.4.1. --- Differential thermal analyzer (DTA) --- p.2-3 / Chapter 2.4.2. --- X-ray powder diffractometry (XRD) --- p.2-4 / Chapter 2.4.3. --- Hot mounting and polishing --- p.2-4 / Chapter 2.4.4. --- Scanning electron microscopy (SEM) --- p.2-5 / Chapter 2.4.5. --- Transmission electron microscopy (TEM) --- p.2-5 / Chapter 2.4.6. --- Vibrating sample magnetometer (VSM) --- p.2-6 / Chapter 2.5. --- References --- p.2-8 / Figures --- p.2-9 / Chapter Chapter 3 --- Effects of sintering temperature on Mg-MgB2 composites --- p.3-1 / Chapter 3.1. --- Introduction --- p.3-1 / Chapter 3.2. --- Experimental results --- p.3-1 / Chapter 3.2.1. --- DTA and XRD analyses --- p.3-1 / Chapter 3.2.2. --- Microstructures --- p.3-2 / Chapter 3.2.2.1. --- Green sample --- p.3-2 / Chapter 3.2.2.2. --- Sample sintered at 550°C --- p.3-3 / Chapter 3.2.2.3. --- Sample sintered at 600°C --- p.3-4 / Chapter 3.2.2.4. --- Sample sintered at 700°C --- p.3-4 / Chapter 3.2.2.5. --- Hexagonal platelets --- p.3-5 / Chapter 3.2.3. --- Superconducting behaviors --- p.3-5 / Chapter 3.2.3.1. --- Critical temperature (Tc) comparison --- p.3-5 / Chapter 3.2.3.2. --- Magnetization loops (M-H loops) --- p.3-6 / Chapter 3.3. --- Discussions --- p.3-7 / Chapter 3.4. --- Conclusions --- p.3-9 / Chapter 3.5. --- References --- p.3-10 / Figures --- p.3-11 / Tables --- p.3-20 / Chapter Chapter 4 --- Effects of composition on Mg-MgB2 composites --- p.4-1 / Chapter 4.1. --- Introduction --- p.4-1 / Chapter 4.2. --- Experimental results --- p.4-1 / Chapter 4.2.1. --- XRD results --- p.4-1 / Chapter 4.2.2. --- Microstructures --- p.4-2 / Chapter 4.2.2.1 --- Mg-0 wt % B (Pure Mg) sintered at 650。C --- p.4-2 / Chapter 4.2.2.2 --- Mg-47 wt % B sintered at 650°C --- p.4-2 / Chapter 4.2.2.3 --- Amount of B in Mg sample --- p.4-3 / Chapter 4.2.2.3.1. --- Overview of Mg-5 to 40 wt % B --- p.4-3 / Chapter 4.2.2.3.2. --- MgB2 phase in different composition (Mg-5 to 47 wt %B) --- p.4-4 / Chapter 4.2.2.3.3. --- MgO phase in different composition (Mg-0 to 30 wt % B) --- p.4-4 / Chapter 4.2.3. --- VSM results (Critical temperature Tc comparison) --- p.4-5 / Chapter 4.3. --- Discussions --- p.4-6 / Chapter 4.4. --- Conclusions --- p.4-8 / Chapter 4.5. --- References --- p.4-10 / Figures --- p.4-11 / Table --- p.4-18 / Chapter Chapter 5 --- Growth Mechanisms --- p.5-1 / Chapter 5.1. --- Introduction --- p.5-1 / Chapter 5.2. --- Brief summary of SEM result --- p.5-1 / Chapter 5.3. --- Growth Mechanism of MgB2 --- p.5-2 / Chapter 5.4. --- Comparison of MgB2 grain size by XRD result --- p.5-7 / Chapter 5.5. --- Stoichiometric Ratio of MgB2 in different temperature --- p.5-7 / Chapter 5.6. --- Growth of the MgB2 platelets --- p.5-8 / Chapter 5.7. --- Conclusions --- p.5-10 / Chapter 5.8. --- References --- p.5-11 / Figures --- p.5-12 / Table --- p.5-15 / Chapter Chapter 6 --- Conclusions and Future Works --- p.6-1 / Chapter 6.1. --- Conclusions --- p.6-1 / Chapter 6.2. --- Future works --- p.6-2 / Chapter 6.3. --- References --- p.6-4

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Thesis (M.Eng.). / Written for the Dept. of Mining and Materials Engineering. Title from title page of PDF (viewed 2009/06/17). Includes bibliographical references.

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Superconductivity in magnesium diboride (MgB2) was first discovered in 2001. It is unique in that it has two superconducting gaps. The transition temperature of 39 K exceeded the maximum transition temperature thought to be possible through phonon mediated superconductivity. Through the study of MgB2, a general paradigm is being formulated to describe multi-gap superconductors. The paradigm includes inter-band and intra-band scattering between the gaps which can cause a smearing of the gap parameter over a distribution instead of a single value. Although each gap is individually thought to be well described by the BCS theory, the interaction between the two gaps causes complications in describing the overall superconducting properties of MgB2. The focus of this work was to lay the groundwork for an MgB2-based Josephson junction technology. This includes improving on a previously established baseline for all-MgB2 Josephson junctions, utilizing the Josephson Effect to experimentally verify a model pertaining to the two-gap nature of MgB2, specifically the magnetic penetration depth, and designing, fabricating, and testing multi-junction devices and circuits. The experiments in this work included fabrication of Josephson Junctions, DC superconducting quantum interference devices (SQUIDs), Josephson junction arrays, and a rapid single flux quantum (RSFQ) circuit. The junctions were all made utilizing the hybrid physical-chemical vapor deposition method, with an MgO sputtered barrier. The current process consists of three superconducting layers which are patterned using standard UV photolithography and etched with Ar ion milling. There were SQUIDS made with sensitivity to magnetic fields parallel to the film surface, which were used to measure the inductance of MgB2 microstrips. This inductance was used in design of more complicated devices as well as in calculating the magnetic penetration depth of MgB2, found to be about 40 nm at low temperature, in good agreement with a previously published theoretical model. Planar-type DC SQUIDs were also made to present the feasibility of the technology for application purposes. The large voltage modulation of over 500 μV at 15 K for these devices along with operation up to 37 K shows that MgB2 is a potential replacement for low temperature devices. The junction series arrays were fabricated with 100 junctions of equal size to present the ever-increasing robustness of the technology. The devices served well to measure the large property spread associated with these junctions and have been well established as a diagnostic tool for improving this spread. The culmination of this work was a basic RSFQ toggle flip flop circuit. A DC measurement of these circuits yielded digital operation up to 180 GHz at low temperature and about 63 GHz at 20 K. This is not yet near the potential limit of MgB2 established by the value of the superconducting gap parameters, but a huge success in showing that MgB2 is a viable option for pursuing superconducting digital electronics suitable for low power, cryogen-free operation. / Physics

Thesis (Ph.D.)--University of Wollongong, 2008. / Typescript. Includes bibliographical references.

Yeung, Him Ching = 以粉末混合方法及夾心樣品方法製作的硼化鎂的特性研究 / 楊謙靖. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Abstracts in English and Chinese. / Yeung, Him Ching = Yi fen mo hun he fang fa ji jia xin yang pin fang fa zhi zuo de peng hua mei de te xing yan jiu / Yang Qianjing. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgments --- p.v / Table of contents --- p.vi / List of table captions --- p.viii / List of figure captions --- p.ix / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Superconductors --- p.1 / Chapter 1.1.1 --- Classifications --- p.1 / Chapter 1.1.2 --- Conventional versus unconventional --- p.2 / Chapter 1.1.3 --- Type I and Type II superconductors --- p.4 / Chapter 1.1.4 --- Critical current Jc and the Bean´ةs Model --- p.5 / Chapter 1.2 --- Magnesium diboride --- p.8 / Chapter 1.2.1 --- Structure --- p.8 / Chapter 1.2.2 --- Physical properties --- p.8 / Chapter 1.2.3 --- Chemical properties --- p.9 / Chapter 1.2.4 --- Conduction mechanisms --- p.9 / Chapter 1.2.5 --- Fabrication methods --- p.9 / Chapter 1.3 --- Objectives of this work --- p.10 / References --- p.12 / Figures --- p.14 / Chapter Chapter 2 --- Methodology and instrumentation --- p.17 / Chapter 2.1 --- Experimental procedures --- p.17 / Chapter 2.2 --- Samples preparation --- p.17 / Chapter 2.2.1 --- Powder mixing approach --- p.17 / Chapter 2.2.2 --- Sandwich structure approach --- p.18 / Chapter 2.3 --- Samples fabrication --- p.18 / Chapter 2.4 --- Determination of compositions --- p.18 / Chapter 2.5 --- Characterization --- p.19 / Chapter 2.5.1 --- X-ray diffractometry (XRD) --- p.19 / Chapter 2.5.2 --- Microstructural analysis --- p.20 / Chapter 2.5.3 --- Magnetic measurements --- p.20 / Chapter 2.5.3.1 --- Setup for Jc measurements --- p.21 / Reference --- p.22 / Figures --- p.23 / Chapter Chapter 3 --- Powder mixing approach --- p.26 / Chapter 3.1 --- Results --- p.26 / Chapter 3.1.1 --- XRD results --- p.26 / Chapter 3.1.2 --- Compositions --- p.27 / Chapter 3.1.3 --- SEM results --- p.28 / Chapter 3.1.3.1 --- Sample sintered at 600°C --- p.28 / Chapter 3.1.3.2 --- Samples sintered at 700°C and 800°C --- p.28 / Chapter 3.1.3.3 --- Sample sintered at 900°C --- p.29 / Chapter 3.1.3.4 --- Sample sintered at 1000°C --- p.29 / Chapter 3.1.3.5 --- Sample sintered at 1050°C --- p.29 / Chapter 3.1.4 --- VSM results --- p.30 / Chapter 3.1.4.1 --- Tc measurements --- p.30 / Chapter 3.1.4.2 --- Hysteresis loops --- p.31 / Chapter 3.1.5 --- Jc measurements --- p.31 / Chapter 3.1.5.1 --- Direct measurement --- p.31 / Chapter 3.1.5.2 --- The Bean´ةs Model --- p.32 / Chapter 3.2 --- Discussions --- p.32 / Chapter 3.3 --- Summary --- p.35 / References --- p.36 / Figures --- p.37 / Tables --- p.47 / Chapter Chapter 4 --- Sandwich structure approach --- p.49 / Chapter 4.1 --- Results --- p.49 / Chapter 4.1.1 --- SEM results --- p.49 / Chapter 4.1.1.1 --- Surface of the Mg disk --- p.49 / Chapter 4.1.1.2 --- Inner region of the Mg disk --- p.50 / Chapter 4.1.2 --- XRD results --- p.50 / Chapter 4.1.2.1 --- Surface of the Mg disk --- p.50 / Chapter 4.1.2.2 --- Inner region of the Mg disk --- p.51 / Chapter 4.1.3 --- VSM results --- p.51 / Chapter 4.1.3.1 --- Tc measurement --- p.51 / Chapter 4.1.3.2 --- Hysteresis loops --- p.52 / Chapter 4.2 --- Discussions --- p.52 / Chapter 4.3 --- Summary --- p.54 / Reference --- p.54 / Figures --- p.55 / Tables --- p.61 / Chapter Chapter 5 --- Growth Mechanism --- p.62 / Chapter 5.1 --- Introduction --- p.62 / Chapter 5.2 --- Brief summary of results --- p.62 / Chapter 5.2.1 --- Powder mixing approach --- p.62 / Chapter 5.2.2 --- Sandwich structure approach --- p.63 / Chapter 5.3 --- Formation of the MgB2 platelets --- p.63 / Chapter 5.4 --- Size of the MgB2 platelets --- p.67 / Chapter 5.5 --- Summary --- p.68 / References --- p.69 / Figures --- p.70 / Tables --- p.75 / Chapter Chapter 6 --- Conclusions and suggestions of future work --- p.76 / Chapter 6.1 --- Summary --- p.76 / Chapter 6.2 --- Future work --- p.77 / Appendix 1 --- p.79 / Appendix 2 --- p.81

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references.