Deposition New Buffer Layers By Polymer Assisted Chemical Solution Approach

Due to the excellent intrinsic electromagnetic characteristics, especially can carry high electric currents in high field magnets, the second generation HTS's REBa₂Cu₃O_x (REBCO) are now attracting much attention in recent years which have widely application prospect. The most significant problems to grow YBCO-coated conductor on NiW tapes are the lattice misfit and the Ni diffusion. A buffer layer is necessary to prevent Ni diffusing and provide a template for the subsequent growth of the YBCO superconducting layer.In this thesis, we deposition the new series of buffer layers REBiO₃ for the coated conductor by chemical preparation approach which offers a large-scale way for the practical applications of coated conductors. To study on the technique of the heat-treatment, we firstly choose single crystal flakes like LaAlO₃/SrTiO₃ as the substrates, then deposit buffer layers on the Ni-alloys tapes. The single crystal substrates with smooth surface and good epitaxy may provide relatively stable template.The major contents are as follows:1. Significant scientific as well as practical interests of the coated conductor research have been introduced, and the fabrications of buffer layer have been studied, especially the chemical solution deposition and the epitaxial growth mechanism.2. The crystal structure, electrical and megnetic properties, and the stability of new buffer layers REBiO₃ have been clarified.3. We studied the fabrication technology of REBiO₃ deposited on single crystal substrate LaAlO₃/SrTiO₃ using different chemical solution deposition.(1) REBiO₃ buffer layers have been deposited on single crystal substrate LaAlO₃/ SrTiO₃ by aqueous polymer-assisted chemical solution deposition (PACSD). YBCO layer has been deposited on YBiO₃/LaAlO₃ by our newly developed fluorite-free MOD and a critical current density J_c (77K, OT) over 3MA/cm² has been obtained with a transition temperature at 90K.(2) A comparison between aqueous polymer-assisted chemical solution deposition (PACSD) and non- aqueous PACSD approaches have been performed, indicating that REBiO₃ thin films with better quality have been obtained via the non-aqueous PACSD approach and the non-aqueous approach itself is of better stability.(3) The epitaxial growth of DyBiO₃ on single crystal substrate has been studied. The influence of the thermodynamic parameters on the phase structure, texture as well as microstructure has been investigated.4. Fabricate REBiO₃ on Ni-5%W alloy tapes by non- aqueous PACSD approach:(1) The process of surface-oxidation epitaxy has been improved;(2) Textured, dense, and smooth REBiO₃ buffer layers have been deposited on Ni-5%W tapes by the non-aqueous PACSD, it is favorable for the subsequent deposition of YBCO in the new structure of coated conductors i.e. YBCO (MOD)/REBiO₃ (MOD)/NiO (SOE)/ NiW.5. Deposit CeO₂ on NiW tapes using the non-aqueous PACSD approach as well as improve the critical thickness of CeO₂ by doping RE elements.