Structural and Electromagnetic Study of Heavily Doped ZR-Added REBCO Coated Conductors Fabricated by Reel-To-Reel MOCVD
High Temperature Superconducting (HTS) Coated Conductors (CCs) based on epitaxial REBa2Cu3O7-δ (REBCO, RE = rare earth) films with superior mechanical strength and high current carrying capacity are being developed for various large-scale electric power and magnetic applications. The critical current density (Jc) of REBCO coated conductors in a magnetic field is higher than that of any other HTS. However, further Jc enhancement in REBCO coated conductors, particularly in fields perpendicular to the tape (B||c) is necessary due to the highly anisotropic nature of REBCO films. The inherently high in-field angular anisotropy of Jc of REBCO CCs can be diminished by introducing Artificial Pinning Centers (APCs) with optimal size, geometry, and density. The incorporation of a high BaMO3 (BMO; M=Zr, Hf, Sn) dopant concentration in REBCO films to achieve a higher density of nanoscale defects has been demonstrated in this work as a very effective strategy to pin the vortices, especially in moderate-to-high applied magnetic fields and low temperatures. Determination of the optimum chemical composition and the REBCO c-axis lattice parameter has been an important objective to create self-assembled growth of elongated perovskite oxide nanostructures at different Zr dopant levels. Maintaining an optimal texture of the epitaxial REBCO film amidst a high density of BMO nanocolumnar defects was another objective. In the present work, REBCO films with 15 and 25 mol.% Zr addition were grown on biaxially-textured templates on metal substrates using a reel-to-reel Metal Organic Chemical Vapor Deposition (MOCVD) method to systematically investigate the self-assembled BZO generated nanorods and the influence of increased Zr content on the texture and superconducting properties. The optimal composition range of 15 and 25 mol.% Zr-added REBCO to achieve the highest self-field and in-field performance has been determined. Also, the influence of REBCO c-axis lattice parameter on the elastic mismatch strain as well as the internal strain in the REBCO matrix surrounded by BZO nanocolumns was investigated. At the same time, the effects of REBCO c-axis lattice parameter on the self-field Jc at 77 K and the in-field Jc at 30 K in applied magnetic fields of 3 and 9 T (B||c) were found. The demonstrated five-fold improvement in REBCO coated conductor performance at 30 K in magnetic fields of 2-3 T accomplished through a systematic study of the influence of heavy doping of Zr in this work can enable future applications of superconducting devices in several rotating machinery applications such as wind turbines and electric motors.
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