【作者】 王威；

【导师】 樊占国；

【作者基本信息】 东北大学 ， 环境科学， 2011， 硕士

【摘要】 第二代高温超导带材——YBa2Cu307一δ(YBCO)涂层导体是目前高温超导材料的研究热点之一,其结构为YBCO超导层/缓冲层(或称隔离层)/金属基带。在众多的缓冲层材料中,CeO2由于与YBCO晶格非常好的匹配性(失配率仅为-0.12%)而成为了最具潜力的外延缓冲层。本论文采用金属有机物沉积(MOD)法结合浸渍涂覆工艺制备了致密的CeO2薄膜作为YBCO单缓冲层,并在其上利用无氟的MOD法直接制备YBCO超导薄膜。具体工作如下采用MOD法在双轴织构的NiW基底上经旋转涂覆制备CeO2单一缓冲层,确定了CeO2薄膜的最佳热处理工艺。利用差示扫描量热法和执重分析(DSC-TG)分析了Ce(CH3COO)3·xH2O的热分解过程,结果表明,220℃之前为Ce(CH3COO)3·xH2O的脱水过程,之后Ce(CH3COO)3开始分解,当温度升到1000℃时,已完全形成了CeO2。讨论了不同的热处理时间和不同的前驱液浓度对CeO2薄膜性能的影响,结果表明：前驱液浓度为0.5mol/L、在1100℃烧结1h制备的Ce02薄膜表面均匀、光滑、平整且致密,具有明显的(200)择优取向,表现出良好的面内织构形式。采用浸涂法在NiW基底上制备了较长的Ce02薄膜样品。研究了干燥过程以及涂覆次数对CeO2薄膜性能的影响。结果表明：涂覆后于30℃下干燥有利于Ce02薄膜(200)晶面的择优生长；多次涂覆制备的Ce02薄膜仍具有良好面外取向,但当涂覆6次时,Ce02薄膜表面出现了很明显的裂纹。通过比较较长样品正反面和不同位置和XRD与表面形貌,得出所制备的双面Ce02薄膜具有很好的两面致性和分布均匀性在CeO2/NiW上采用无氟的MOD法制备了YBCO超导层。研究了所氛、热处理时间及涂覆方式等因素对YBCO薄膜性能的影响。结果表明：即使在还原性Ar-2%H2气氛下Ni基底仍会被氧化形成NiO,而YBCO超导相的合成需要一定的氧分压。采用浸涂法在O2气氛下750℃烧结3h的YBCO薄膜具有(00l)择优取向,表面致密、颗粒分布均匀,具有较低的室温电阻。更多还原

【Abstract】 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.更多还原