Preparation And Property Of YBCO High Temperature Superconducting Thin Films With Oxide Nanostructure

High critical current density Jc is one of the most important requirements for practical applications of superconductors. High temperature superconductors (HTS) usually have large values of Jc at low temperatures in applied magnetic field. But Jc decreases quickly with the increase of temperature. One of the main reasons is that HTS typically lacks effective flux pinning centers.Superconducting properties of YBCO thin films can be greatly improved by introducing densly distributed crystalline defects as flux pinning centers in YBCO matrix. Introduction of artificial pinning centers (APCs), which have a scale of nanometers (comparable to the coherence length), is the effective approach to enhance Jc.In this work, a small amount of non-superconducting RxOy (BaZrO3 or Y2O3) second-phase nanoparticles was incorporated into epitaxial YBCO thin films as the APCs. Three types of second-phase nanoparticles were prepared in epitaxial YBCO thin films. Different approaches introducing different types of APC's for impacting on epitaxial grown and superconducting properties of YBCO thin films are studied.At first, we used the solid-state reaction method to synthesize YBCO and BaZrO3 (BZO) compounds, and sintered the YBCO targets containing 1.5vol% of RxOy, a pure YBCO, and a pure Y2O3 target. The prepared powders and target materials were tested and analyzed to ensure high quality of superconducting tagret materials was obtained.Different approaches have been employed to introduce the three types of APC's into YBCO thin films grown by pulsed laser deposition (PLD) in this work. The first approach was implemented by ablating a YBCO composite target comprising a small percentage of second-phase BZO. During the growth of YBCO films, the influence of the PLD parameters on the epitaxial growth characteristics and superconducting properties of YBCO thin films was investigated. In the second approach, the substrate was first decorated with the second-phase nano-Y2O3 islands before the deposition of YBCO thin films. By controlling the number of laser pulses and other deposition parameters, Y2O3 nanoislands have been successfully fabricated on the LaAlO3 (LAO) substrates prior to the deposition of YBCO-BZO thin films. The third approach was the multilayer YBCO thin films containing BZO and Y2O3 nanostructured APCs, comprising alternating YBCO-BZO five layers and YBCO-Y2O3 five layers. One way to implement the multilayer approach is to ablate a pure YBCO target and another pure second-phase target in an alternating sequence to grow multilayered YBCO thin films. The films thickness all above was about 300nm.The epitaxial characteristics and microstructural morphologies of the YBCO thin films grown under different manners above were analyzed with X-ray diffraction, Atomic Force Microscopy and Scanning Electronic Microscopy techniques. The superconducting properties especially critical current density Jc in high magnetic field under 77K of these YBCO thin films were measured. The high quality superconducting thin films were obtained.