Fabrication Of BaZrO₃/NiO Buffer Layer For YBCO Coated Conductors

YBa₂Cu₃O_7-?(YBCO)coated conductors have attracted much attention due to its excellent current-carrying property under high magnetic fields.However,several problems such as lattice mismatch and inter-diffusion can be caused if YBCO films are directly deposited on the flexible metal NiW tapes.Therefore,it is necessary to prepare a buffer layer film between the NiW substrates and the superconductor layer which can serve as an epitaxial growth template for YBCO film and also as a barrier for blocking the diffusion of elements.The traditional buffer layer are mostly constructed by the multilayer structure,which leads to the complicated fabrication processes and the difficulties in a large scale.Therefore,in this study,a kind of simplified buffer layer architecture which was prepared by Self-Oxidation Epitaxy(SOE)in combination with sol-gel has been developed Using this simplified buffer architecture the high c-axis textured YBCO film can be easily prepared on the NiO buffer layer.The main research contents and results are summarized as follows:Firstly,the process of self-epitaxial growth of NiO on the NiW baseband was studied.It was found that NiO films with good c-axis orientation and low surface roughness can be prepared under the conditions of O₂:N₂=1:250,oxidation temperature of 950? and oxidation time of 5 minutes.After XRD scanning analysis and EBSD analysis of scanning electron microscopy,it was confirmed that the prepared NiO has good(200)orientation,meanwhile has good in-plane and out-of-plane growth texture.Secondly,BaZrO₃(BZO)was prepared by sol-gel method to improve the surface roughness of NiO and prevent diffusion.It was found that BZO sols with a total metal ion concentration of 0.3mol/L were used as precursor,after the gel film has been pretreated(80? and 200? for 10min respectively),then heat-treated at 850? for 1 hour,and we can obtain BZO films with good c-axis orientation on the lanthanum aluminate single crystal substrate.This will lay the foundation for the deposition of BZO films on NiO.Thirdly,Using the same pretreatment technology,the BZO film with good c-axis orientation can be prepared on the NiO/NiW composite film when the sample was heated up to 850? in the furnace and holding for 30 minutes,there by forming a BZO/NiO/NiW composite structure.The results show that the roughness of the prepared BZO film(Sa=17nm)was improved compared with the original NiO(Sa=26nm),and this will help to promote the growth of YBCO film with c-axis texture.Finally,a YBCO thin film was prepared by pulsed laser deposition on the BZO/NiO/NiW composite structure,XRD results show that it had a good c-axis orientation.It will lay the good foundation for simplifying the buffer architecture of YBCO coated conductor in the future.