Ic大于1000A/cm的高Jc REBCO掺杂厚膜的微结构与超导物性之间的关系

YBCO high temperature superconductor tapes have wide applications in electrical power transportation, medical clinical devices and maglev transportation, etc. One of the requirements for practical applications of HTS films is the high value of the critical current density. The main bottleneck for YBCO tape application is the property/price ratio. For this purpose, how to fabricate YBCO tapes with over 1000A Ic along 1cm width is one of the most significant topics in this field. We can not increase the critical current Ic by simply increasing the thickness of the superconducting films because of the thickness dependence of the epitaxial superconducting films. This project figures on repressing the thickness dependence through inducing the nano-scale defects during the fabrication of superconducting films. Furthermore the size of artifical pining defects correspond to the superconducting coherence length, and so can act as effective artificial flux pinning centers which enhance the superconducting performance under magnetic field. So this project has theoretical guiding value on the fabrication of the practical REBCO superdoncuting tape with high performance. We fabricate the MgO thin film with biaxial texturing by ion beam assisted deposition (IBAD) and then deposite the superconducting films with different thickness by plused laser deposition( PLD). We study the doped with different rare earth and nano-particles and multilayers structure, reveal the thickness dependence of REBCO films, illustrate the related transport mechanism through studying the superconducting physical properties and analyzing the microstructure. Through the above studies, it is anticipated that the performance of the superconducting films will be graetly improved and can develop fabrication processes for REBCO tapes with high critical current density and over 1000A/cm performance.

YBCO第二代高温超导带材在电力、医学和交通等领域具有广泛的应用前景。应用的主要瓶颈是如何大幅提高性价比，研制Ic达到1000A/cm(77K,自场)以上的YBCO带材是该领域目前关键科学问题之一。由于外延生长超导薄膜时存在厚度效应，所以无法通过简单增加膜厚的方法来增加Ic。本项目通过在薄膜制备过程中人工引入纳米颗粒抑制厚度效应。此外，以人工方式引入的纳米缺陷态因其尺寸与超导相干长度相当，还可作为有效的磁通钉扎中心来提高外场下的超导性能。该项目对高性能实用型REBCO超导带材制备具有理论指导意义。本项目采用IBAD方法在金属基底上制备双轴织构MgO薄膜，采用PLD方法制备不同厚度超导膜。通过不同稀土元素掺杂和第二相纳米颗粒复合掺杂以及多层膜结构，揭示REBCO薄膜厚度效应，通过超导物性研究与微结构分析阐明与之相关联的输运机理。通过抑制厚度效应大大提高载流能力，实现>1000A/cm的目标。

以(REBa2Cu3O7-x)(Re=Y,或 Gd, Sm等稀土元素，简称为REBCO)为基础的第二代高温超导带材具有电流密度高、交流损耗小和机械强度高等优点，从而拥有广阔的应用前景。目前已经突破带材制备技术，可以批量生产。但是，仍有一些问题急需解决，比如制备厚REBCO薄膜，理解材料科学设计钉扎中心。.为此，本项目开展了以下几个方面的研究：1）IBAD-MgO基底上单一CeO2隔离层的制备研究；2）稀土元素替代和掺杂对REBCO超导薄膜的影响；3）REBCO超导薄膜厚膜研制和厚度效应研究；4）第二相掺杂对REBCO超导薄膜的影响；5）REBCO/CeO2/REBCO和REBCO/STO/REBCO多层膜制备研究。.通过本项目的研究，取得了以下主要研究成果：（1）在IBAD-MgO基底上制备出高质量的单一CeO2隔离层，面内织构仅为2.7°。（2）确定了特色的超导薄膜的成分为Y0.5Gd0.5Ba2Cu3O7-x（YGBCO）。（3）研制出沉积温度（400-800 ℃）、氧分压（5-200 mTorr)和厚度（10-160 nm）范围都很宽的STO夹层制备工艺，YGBCO/STO/ YGBCO多层膜具有良好的C取向和光滑表面，适合于超导厚膜制备。（4）发现5% BHO掺杂YGBCO超导薄膜具有优良的磁场下性能。（5）提出种子层技术和分层制备技术，抑制了超导层的厚度效应，制备出3.5微米厚的YGBCO薄膜，在77 K、自场条件下临界电流达到1075 A/cm。(6) 通过种子层技术提高了5% BHO掺杂YGBCO超导薄膜的临界电流密度，临界电流密度从2.5 MA/cm2 提高到了4 MA/cm2。本项目阐明了厚度效应、钉扎类型和钉扎效果，为进一步提高超导薄膜的载流能力提供科学依据。