Abstract:The preparation of a YBa 2 Cu 3 O 7−x /LaNiO 3 /YBa 2 Cu 3 O 7−x sandwich structured film on a LaAlO 3 (100) substrate by a sol-gel method was investigated. YBa 2 Cu 3 O 7−x /LaNiO 3 /YBa 2 Cu 3 O 7−x tri-layer heterostructures with different epitaxial characteristics can be deposited by controlling the heat treatment temperature. X-ray diffraction and transmission electron microscopy results show that the bottom YBCO film grows epitaxially on the LaAlO 3 substrate along the c axis, and that this epitaxial growth trend is extended to the subsequently deposited LaNiO 3 film. For this reason, the LaNiO 3 film also grows epitaxially along the c axis. Furthermore, this epitaxial growth trend is extended to the top YBa 2 Cu 3 O 7−x film, yielding YBa 2 Cu 3 O 7−x /LaNiO 3 /YBa 2 Cu 3 O 7−x tri-layer heterostructures with epitaxial growth characteristics along the c axis, which enables both the bottom and top YBa 2 Cu 3 O 7−x layers to possess superconducting abilities.
YBa2Cu3O7-x (YBCO) films were prepared on single-crystal LaAlO3 (100) substrate using a low-fluorine sol-gel method. The effect of the oxygen content in the atmospheres of heat treatment at 725 °C on the critical current density (Jc) of the obtained YBCO films was investigated. Results show that all the films heat-treated in the oxygen content range of 100~1700 µL/L exhibit good biaxial-texture characteristics. However, high-Jc YBCO films are not obtained at the oxygen contents of 100 and 200 µL/L due to the lower density of the surfaces. With increasing the oxygen content, the film surface becomes dense gradually. When the oxygen content is 300 µL/L, the surface of the film is very dense and Jc reaches 4.3 MA/cm 2. Furthermore, many copper-rich second phases grow up on the surfaces with further increasing oxygen content up to 800 and 1700 µL/L, which is a dominant reason for the decline in Jc of the films.
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