Second-generation High-temperature Superconducting Dc Magnetron Sputtering With Material Cyc Oxide Buffer Layer

Due to its lower ac loses, better in-field performance, and lower processing costs over first-generation high-temperature superconductor(HTS) tapes, second-generation YBa2Cu3O7-δ(YBCO) HTS tapes (also called coated conductors) attract the attention of the reserchers worldwide. The main difficulties in fabricating coated conductors are lattice mismatch and the diffusion of oxygen and metal atoms. It is necessary to deposite buffer layers between flexible metal substrates and YBCO layer. To ensure that buffer layers can work as a good template for growing YBCO layer and block the diffusion efficiently, buffer layers must be c-axis oriented, well textured, smooth, dense and crack free. The fabrication of buffer layers on rolling-assisted biaxially textured substrates(RABiTS) was studied in this thesis.The most commonly used architectre consisted of CeO₂(cap layer)/YSZ(barrier layer)/CeO₂(seed layer). CeO₂ seed layer was deposited on the RABiTS Ni-5at%W alloy with two different methods: In-situ Post-Annealing Texture(IPAT) technology and reactive sputtering. With opitmum IPAT technics parameters, CeO₂ thin film has shown c-axis single oriented. The full width at half maximum(FWHM) of in-plane and out-of-plane scan are 6.1°and 8.4°, respectively. The root mean square roughness is no more than 4nm. The smaller FWHMs of in-plane and out-of-plane scan (4.6°and 3.1°) were obtained by using reactive sputtering. The relationships of parameters (anealing temperature, annealing time, substrate temperature, power, and H₂O pressure) and the structure, suface morphology of thin film were discussed.YSZ barrier layer and CeO₂ cap layer were grown on CeO₂/NiW by using reactive sputtering. Through optimizing the parameters(substrate temperare, H₂O pressure), c-axis single oriented YSZ and CeO₂ thin films were obtained. Their FWHMs of in-plane and out-of-plane scan were less than 5.5°and 4.0°. Secondary ion mass spectrometry was employed to analyze the depth profile of buffer layers. It showed that the diffusion had been blocked effeciently by buffer layers.YBCO thin film was epitaxially grown on CeO₂/YSZ/CeO₂/NiW. Its FWHMs of in-plane and out-of-plane scan were 6.2°and 4.6°. It meant that buffer layers had provided a good template for YBCO.