Research On Preparation Of CeO₂Single Buffer Layer And YBCO Layer With MOD Method

The second generation high temperature superconducting tapes——YBa2Cu3O7-δ(YBCO) coated conductor is one of the focus in the field of high temperature superconducting materials, with its architecture of YBCO superconducting layer/buffer layer (i.e.barrier)/metallic substrate. Among those buffer layers, CeO2becomes the most potential buffer layer materials due to the lattice mismatch with YBCO is only-0.12%. In this paper dense CeO2layer was dip-coated on NiW substrates with metal organic deposition (MOD) method and YBCO superconductor films were directly deposited on CcO2layer with fluorine-free MOD. The study results were as follows:CeO2single buffer layer was prepared with MOD by spin-coating. The optimal parameters of heat treatment process were determined. The thermal decomposition process of Ce(CH3COO)3.xH2O was analyzed by thermo-gravimetric (TG) and differential scanning calorimeter (DSC). The results showed that the dehydration process of Ce(CH3COO)3.xH2O terminated at220℃. After dehydration, Ce(CH3COO)3began to decompose. When the temperature was up to1000℃, it completely transformed to CeO2. The effects of concentration of precursor solutions and holding times of sintering on the properties of the films were investigated. The results showed that CeO2thin films sintered at1100℃for1h with the concentration of0.5mol/L represented good out-of-plane orientation and in-plane texture, and their surface morphology was dense and crack-free.Long CeO2single buffer layer was prepared with MOD by dip-coating. The effects of drying process and coating frequencies on the properties of the films were investigated. The results showed that it was beneficial to the growth of (200) preferred orientation when the original films were dried at130℃after coating. Even coating multiple times on NiW substrates, the obtained CeO2films still represented good out-of-plane orientation. However, the cracks formed on the CeO2buffer layer when the substrates were coated6times. Both sides of CeO2buffer layer showed good texture and different parts of the long samples held well uniformity.YBCO superconductor layer was coated on CeO2/NiW with fluorine-free MOD. The effects of atmosphere, holding times and coating methods on the properties of YBCO films were investigated. The results showed that Ni was still oxidized even in reducing atmosphere (Ar-2%H2), and adequate oxygen partial pressure is necessary for the synthesis of YBCO superconducting phase. YBCO films sintered at750℃for3h by dip-coating under O2atmosphere showed (00l) preferred orientation and their surface morphology was dense with low room temperature resistance.