Growth and characterization of nanocomposite yba2cu3o7-δ – bamo3 (m = zr, hf) thin films from colloidal solutions

Resumo

YBa2Cu3O7-δ (YBCO) is the best material choice to address the performances required in power applications and magnets working under high magnetic fields. However, it is still challenging to achieve low manufacturing costs and high superconducting performances of coated conductors (CCs) for large scale power applications. Chemical Solution Deposition has emerged as a very competitive technique to obtain epitaxial films and multi-layers of high quality with controlled nanostructures. We have developed a novel Flash Heating growth process that shows high potential to be compatible with the industrial reel-to-reel production of YBCO CCs. Here we have set up, for the first time, a full image describing the intermediate phase and microstructure evolution during this heating process. We extend the growth temperature window down to 750 ºC without any degradation of superconducting properties, making it being compatible with the deposition of YBCO CCs on CeO2-caped metallic tape substrates. In addition, we have also found that this growth process promotes the formation of a high concentration of stacking faults and so of nanostrain. YBCO and nanocomposite ultrathin films, in the range of 5-50 nm, have been prepared after a series optimization of growth parameters. The relief of the interfacial energy induces a high density of stacking faults, leading to a highly distorted YBCO matrix. Such microstructural disorder becomes extremely serious when the film thicknesses decrease below 25 nm, significantly degrading the superconductivity. We have also studied the evolution of the characteristics of spontaneous segregated nanoparticles with nanocomposite film thicknesses and their influence on the vortex pinning efficiency. The preparation of YBCO nanocomposites from non-reactive preformed oxide nanoparticles forming colloidal solutions has demonstrated to be a very successful strategy to achieve a tight control of the nanoparticle characteristics and the optimized nanostructural landscape on the superconducting films. BaMO3 (M=Zr, Hf) perovskites are shown to be the most promising compositions of preformed nanoparticles up to now that led to high quality nanocomposite films at high nanoparticle concentrations (20-25 mol%). The composition and size of nanoparticles have demonstrated to be crucial factors for tailoring vortex pinning performance in applied magnetic field. The application of the Flash Heating growth process in the growth of nanocomposite films allows both the preservation of nanoparticle size and the generation of a high density of short stacking faults, which play a synergistic effect to increase the artificial pinning centers and enhance the strong pinning contribution. Multi-deposition technique is proved effective to further enhance the film thickness while vortex pinning efficiency is preserved and current-carrying capacity of the nanocomposite films is increased.