Tuning the Superconducting Properties of Magnesium Diboride Doctoral thesis

摘要

This work is presented in the following order: A review of the relevant physics and discussion of theoretical predicitions for a two gap superconducting compound is given in chapter 2. Chapter 3 provides a review of the baic properties of MgB(sub 2). Details of sample synthesis and characterizatin are given in chapter 4. Chapter 5 present normal state and superconducting properties of Mg(B(sub 1-x)C(sub X)(sub 2) wires. Attempts to increase critical current densities in filaments via titanium additions are discussed in chapter 6. In chapters 7 and 8 alternative methods for synthesizing doped MgB(sub 2) powders are explored. In chapter 7 we synthesize Mg(B(sub 1-x)C(sub x))(sub 2) up to x=0.069 using a mixture of Mg, B, and the binary compound B(sub 4)C. Chapter 8 explores an alternative method, plasma spray synthesis, to produce nanometer sized doped boron powders for powder-in-tube applications. The effects of neutron irradiation on pure MgB (sub 2) wire is discussed in chapter 9. This is followed by a study of the effects of neutron irradiation on Mg(B(sub .962)C(sub .038))(sub 2) wires, presented in chapter 10. I will summarize the results of all of these studies in chapter 11 and discuss future directions for research in understanding the physics behind this novel material as well as its development for practical applications. In this thesis I have presented the results of investigations into the changes in the superconducting properties of MgB(sub 2) as a function of carbon doping and neutron irradiation. The goal has been to understand the physics underlying this unique two-gap superconductor as different types of perturbations are made to the syste. Such knowledge not only contributes to our understanding of two-gap superconductivity, but could potentially lead to the development of superconducting MgB(sub 2) wires for the use in power applications near 20 K.