Growth orientation and superconducting properties of YBa2Cu3O7−δ films prepared by the low-fluorine sol-gel process
Growth orientation and superconducting properties of YBa2Cu3O7−δ films prepared by the low-fluorine sol-gel process
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DOI：
10.1088/1674-4926/31/8/083004
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发表时间：
2010-08
影响因子：
5.1
通讯作者：
Lei Li;Zhao Gao-yang;X. Hui;Zhao Juanjuan
中科院分区：
文献类型：
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作者：
Lei Li;Zhao Gao-yang;X. Hui;Zhao Juanjuan
采用低氟溶液浸渍提拉法在(10 0)取向的LaAlO_3(LaO)单晶衬底上制备了YBa2Cu3O7−δ薄膜。借助X射线衍射仪、扫描电子显微镜和高分辨电子显微镜对其微观结构进行了表征。用标准的四探针法测量了它们的超导性质。实验结果表明，在足够高的湿度条件下得到的薄膜比在相对低湿度条件下得到的薄膜具有更好的c轴织构和超导性能。基于经典成核和化学反应热力学理论，结合我们的实验结果，解释了YBCO薄膜在一定湿度条件下的结晶和生长机制。结果表明，在YBCO晶界聚集的BaF2和CuO等未反应中间相将引起YBCO晶格畸变，并在晶化过程中诱导形成a轴取向的YBCO晶体。因此，认为热处理气氛中水蒸气的相对含量对制备具有良好超导性能的c轴取向的YBCO薄膜起着相当重要的作用。
YBa2Cu3O7−δ (YBCO) films were deposited on (100)-oriented LaAlO3 (LAO) single crystal substrates by the dip-coating process using low-fluorine solution. Their microstructures were characterized with the aid of X-ray diffractometry, scanning electron microscopy and high-resolution transmission electron microscopy. Their superconducting properties were measured by the standard four-probe method. The experiment results show that the film obtained under high enough humidity conditions exhibits better c-axis texture and superconducting properties than the film under a relatively low humidity conditions. Based on the classical nucleation and chemical reaction thermodynamics theory, the underlying crystalline and growth mechanisms of YBCO films under certain humidity conditions are explained in combination with our experimental results. It is suggested that the unreacted intermediate phases such as BaF2 and CuO aggregated in the YBCO grain boundary will cause lattice distortion in the YBCO matrix and further induce the formation of a-axis oriented YBCO grains as crystallization proceeds. Therefore, it is believed that the relative content of water vapor within the heat-treatment atmosphere plays quite an important role in the preparation of c-axis oriented YBCO film with good superconducting properties.