Solution processing of YBa2Cu3O7 from the trifluoroacetates route has been proved successful to prepare cost-effective superconducting films with high critical currents. Importantly, this approach offers many new opportunities to continue improving the film performance upon tight control of the molecular precursors transformation to the intermediate nanocrystalline phases formation, the generation of nanoscale defects, and the conversion to crystalline, epitaxial films. Here we have explored two of these aspects, first, the influence of the kinetics on the transformation of the intermediate phases to the epitaxial YBa2Cu3O7 by designing a phase diagram of the intermediate phase evolution and second, the control of artificial secondary phases (size, composition, concentration) on the generation of microstructural defects and vortex pinning.
We demonstrate that a fast kinetic transformation of the intermediate polycrystalline phases, Ba1-xYxF2+x and CuO, through a heating rate 30 times faster than the conventional route boosts the nucleation, minimizes the coarsening of the intermediates and generates nanometric structural defects named intergrowths. This cascade of phenomena contributes to decreasing the overall processing temperature and enhance the performance at high magnetic fields. This fast processing route has been adopted to subsequently explore the effect of incorporating artificial nanosized secondary phases in the YBCO to prepare epitaxial and superconducting nanocomposites. Pre-formed BaHfO3 and BaZrO3 nanoparticles with a size ranging from 5 nm to 10 nm has been added ( 0-25 % mol) in the YBCO precursor solution and fast converted to epitaxial nanocomposite films. 7 nm nanoparticles generate high density of intergrowth both contributing to enhance the artificial vortex pinning. Additionally, the preparation of a YBCO seed layer prior to nanocomposite deposition ensures a well-dispersed distribution of the nanoparticles within the YBCO matrix throughout the film thickness maximizing the pinning efficiency. These studies allowed us to overcome important synthetic challenges in YBCO preparation and better understand the role of kinetics and nanosized defects in the superconducting film putting forward a cost-effective route to further disentangle the underlying physics of high temperature superconductors for power applications.
Control of nanostructure and pinning properties in solution deposited YBa2Cu3O7−x nanocomposites with preformed perovskite nanoparticles
Ziliang Li, Mariona Coll, Bernat Mundet, Natalia Chamorro, Ferran Vallès, Anna Palau, Jaume Gazquez, Susagna Ricart, Teresa Puig, Xavier Obradors
Scientific Reports 9, 5828, 1-14, 2019
Accelerated growth by flash heating of high critical current trifluoroacetate solution derived epitaxial superconducting YBa2Cu3O7 films
Ziliang Li, Mariona Coll, Bernat Mundet, Anna Palau, Teresa Puig, Xavier Obradors
Journal of Materials Chemistry C 4748-4759, 2019
Figure: High performance YBCO thin films by solution deposition strongly depends on the presence of nanosized defects (nanoparticles, structural defects) which can be tuned by the processing conditions