Progress in superconducting REBa2Cu3O7 (RE = rare earth) coated conductors derived from fluorinated solutions

Abstract

In this work, we review recent progress achieved in the use of chemical solution deposition (CSD) based on fluorinated metalorganic precursors to grow superconducting REBa2Cu3O7 (REBCO) films and coated conductors (CCs). We examine, first of all, the advances in optimizing the steps related to the solutions preparation, deposition and pyrolysis based on novel low-fluorine metalorganic solutions. We show that a new type of multifunctional colloidal solutions including preformed nanoparticles (NPs), can be used to introduce artificial pinning centers (APCs). We analyze how to disentangle the complex physico-chemical transformations occurring during the pyrolysis with the purpose of maximizing the film thicknesses. Understanding the nucleation and growth mechanisms is shown to be critical to achieve a fine tuning of the final microstructure, either using the spontaneous segregation or the colloidal solution approaches, and make industrially scalable this process. Advanced nanostructural studies have deeply modified our understanding of the defect structure and its genealogy. It is remarkable the key role played by the high concentration of randomly distributed and oriented BaMO3 (M = Zr, Hf) NPs which enhance the concentration of APCs, such as stacking faults and the associated partial dislocations. Correlating the defect structure with the critical current density Jc (H,T,θ) allows to reach a tight control of the vortex pinning properties and to devise a general scheme of the vortex pinning landscape in the whole H–T phase diagram. We also refer to the outstanding recent achievements in enhancing the vortex pinning strength by shifting the carrier concentration in REBCO films towards the overdoped state, where the pinning energy is maximum and so, record values of critical current densities are achieved. This confirms the performance competitiveness of nanocomposite CCs prepared through the CSD route. We conclude with a short summary of the progress in scaling the CC manufacturing using fluorinated solutions.