Enhanced High-Field Flux Pinning in YBa2Cu3O7-x Thin Films Through Engineering of Ba2YTaO6 Artificial Pinning Centres

Abstract

Commercial coated-conductor tapes based on the high-temperature superconductor YBa2Cu3O7 are considered essential for fabricating high-field compact fusion magnets. An essential aspect in the development of these magnets is an understanding of the most effective pinning centre materials at low temperatures (10 K – 30 K) and high magnetic fields (B > 10T) for enhancing the critical current densities of these materials. This thesis investigates the effectiveness of the double perovskite material Ba2YTaO6 in enhancing the critical current density of YBa2Cu3O7 thin films grown by pulsed laser deposition. The first chapter of work investigates the structural and superconducting properties of commercial coated conductors produced through various manufacturing methods. Following the study of commercial films, the following chapters present the results of investigations into the pinning effects of Ba2YTaO6. A range of pinning morphologies are produced from this material which are used to determine the optimal pinning centre morphology for enhancing the performance of YBa2Cu3O7 films under the conditions required for fusion magnets. The critical current densities of these films are correlated to their structural and morphological properties. The studies of Ba2YTaO6-doped YBa2Cu3O7 presented here first report the optimal deposition frequency and volumetric dopant concentration of Ba2YTaO6 and then further investigate the pinning effects of mixed pinning centre morphologies based around Ba2YTaO6. The final chapter of this work reports on attempts to introduce Ba2YTaO6 pinning centres into YBa2Cu3O7 thin films grown by established liquid-assisted processing techniques, essential for its application in commercial films where high growth rates are required. A mixed Ba2YTaO6 + Y2O3 pinning centre morphology grown at intermediate deposition frequencies of 5 and 10 Hz is found to result in YBa2Cu3O7 thin films which exhibit critical current densities similar to the best reported literature data at 77 K, 10 T and 10 K, B > 10 T.