Growth and superconducting properties of (RE)Ba2Cu3O7-d single grain superconductors containing nano-size dopants

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Melt processed, single grain high-temperature (RE)-Ba-Cu-O superconductors, where RE is a rare-earth element such as Nd, Sm, Eu, Gd or Y, are known to be able to generate high magnetic fields due to their unusually high critical current densities and their high irreversible fields. Therefore, they have significant potential for a range of practical applications, including MRI, maglev, flywheel energy storage, motors and generators. The critical current density Jc is a structure-sensitive parameter, which is dependent critically on the sample's microstructure. In particular, Jc is proportional to the number of pinning centres per unit volume in the superconducting phase. Non-superconducting phases with small dimensions (in the nanometer range) within the superconducting matrix form particularly effective flux pinning centres in (RE)BCO. By inserting nano-size dopants, Jc can potentially improve significantly. The doping of (RE)BCO includes two particular challenges: The first challenge is the fabrication of bulk superconductors in the form of a single grain, which is effectively a single crystal. The advantage of single grains is the absence of grain boundaries, which lead to resistance and dissipation and therefore lower the amount of current in the superconductor. Standard (RE)BCO single grains grow typically through a complicated process including a peritectic reaction, seeding and slow cooling. The introduction of nano-size dopants may make the growth process of single-grain (RE)BCO an even more time-consuming and complicated task. The second challenge is the investigation of the nature of the nano-sized particles, or inclusions in the superconducting matrix, including distinguishing the types of particles from composition analysis that overcome the limitations of conventional Energy-dispersive X-ray spectroscopy (EDX). This will form the basis of correlating the distribution of nanoparticles to local Jc in target (RE)BCO materials. This PhD project will focus on the fabrication of single grains of (RE)-Ba-Cu-O bulk superconductors containing nano-size dopants, such as RE2O3. It can be anticipated that doping of (RE)-Ba-Cu-O will improve its superconducting properties. In addition to analysing the microstructures of the single grain samples using optical microscopy, this PhD project will also focus on analysing the nano-sized phases quantitively using scanning electron microscopy and other advanced instrumental techniques. The project will correlate Jc and the key microstructural features identified above to enable a deeper understanding of flux pinning in (RE)BCO single grain materials.