Enhancing the flux pinning of high temperature superconducting yttrium barium copper oxide thin films

Date of Award

2017

Degree Name

Ph.D. in Materials Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Advisor: P. Terrence Murray

Abstract

Superconductors’ unique properties of zero resistance to direct current at their critical temperatures and high current density have led to many applications in communications, electric power infrastructure, medicine, and transportation. Yttrium barium copper oxide, YBa2Cu3O7-δ, (YBCO) is a Type II superconductor, whose thin film’s high current density results from pinning centers associated with point defects from oxygen vacancies, and with twin and grain boundaries. Addition of second-phase inclusions enhances flux pinning and current density by incorporating additional pinning centers. This research systematically studies the effect of nanoparticle pinning with the addition of an insulating, nonreactive phase of Y2BaCuO5 (Y211). While many previous studies focused on single phase additions, the addition of several phases simultaneously shows promise in improving current density by combining different pinning mechanisms. This research systematically studies the following mixed phase additions to YBCO targets to produce thin films by pulsed laser deposition (PLD): YBCO + BaZrO3 + Y2O3,YBCO + BaHfO3 + Y2O3, YBCO + BaSnO3 + Y2O3, and YBCO + BaSnO3 + Y211. Thin films are prepared by pulsed laser deposition on LaAlO3 and SrTiO3 substrates. Processing parameters vary the volume percent of dopants present in the target and the deposition temperatures of the films to optimize critical current densities. Results and comparisons of flux pinning mechanisms, current densities, critical temperatures, and microstructures will be presented in detail. In short, the 10 vol. % Y211 doped YBCO films achieved the highest current density, and coincidently also possessed the least amount of lattice mismatch and the least amount of difference of thermal expansion coefficients between the dopant and YBCO. Mathematical modeling will address the strong anisotropic and weak isotropic flux pinning contributions of the doped YBCO films. The Y211 doped YBCO films were the only dopant system studied which increased both the isotropic weak and anisotropic strong flux pinning contributions. This work contributes to a greater understanding for future optimizations of YBCO doped films with pinning landscapes tailored for high current and high field applications at various field orientations.

Keywords

Flux pinning, Superconductors Density, Pulsed laser deposition, Engineering, Materials Science, Yttrium Barium Copper Oxide, type II superconductors, flux pinning, current density, nano particle inclusions, pulsed laser deposition

Rights Statement

Copyright © 2017, author

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