Date of Award

12-2020

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Dr. Asghar Kayani

Second Advisor

Dr. Arthur McGurn

Third Advisor

Dr. Lisa Paulius

Fourth Advisor

Dr. Ulrich Welp

Keywords

Critical current, high-temperature superconductors, ion beam irradiation induced defects

Abstract

Particle irradiation is used to induce defects in high-temperature superconducting Y1Ba2Cu3O7-x (YBCO) coated conductors, containing predominantly c-axis oriented barium zirconate (BZO) nanorods as pre-existing vortex pinning defects. Samples are irradiated with 50.0 MeV Cu ions with doses of 2.5 x 1012, 2.0 x 1012, 1.5 x 1012, 1.0 x 1012, 0.75 x 1012, 0.5 x 1012, 0.05 x 1012 ions/cm2. The dose of 0.5 x 1012 ions/cm2 is found to be the optimal dose with a moderate enhancement of critical current density (Jc) in high fields (>5 T) at 5 K, while suppression of Jc is observed for other doses at all fields and temperatures. Post-irradiation annealing at 150o C for 30 minutes in the oxygen atmosphere recovered not only the transition temperature (Tc), which is expected, but also Jc, which was hugely suppressed by Cu irradiation. Also, the incident angle of irradiation is implemented as a new parameter for optimizing vortex pinning in the material. Samples are irradiated at angles of 0o, 15oand 30o from the crystallographic c-axis. It is found that irradiation at 30o leads to a moderate enhancement of Jc at 5 K in high fields (> 2 T). In contrast, Jc is suppressed for all temperatures and fields for other angles of irradiation. Furthermore, Irradiation with 12.0 MeV oxygen with a dose of 1 x 1013 ions/cm2 is also carried out in YBCO single crystal and coated conductor. The enhancement in the magnetization after oxygen irradiation at 5 K, 27 K, 45 K, and 77 K in YBCO single crystal in low fields is observed. However, in the YBCO coated conductor, no significant enhancement is seen.

The transport studies of the coated conductor bridge sample are also carried out. From the angular dependence of resistance (R Vs. θ) graph, anisotropic peaks are observed, which implies the presence of correlated pinning centers, which are not aligned with the main crystallographic directions. Furthermore, 12.0 MeV oxygen irradiation with a dose of 1 x 1013 O-ions/cm2 is carried out. The temperature dependence of the resistance (R Vs. T) showed kinks in fields 1 T and 2 T after irradiation, implying the possible hopping of the vortices happened due to a competition between irradiation-induced defects and pre-existing defects. Finally, Ic lines obtained from I-V curves show a slight shift towards lower temperature, which suggests that 12.0 MeV oxygen irradiation at the dose of 1 x 1013 O-ions/cm2 suppresses the critical current in the sample.

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Dissertation-Open Access

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