异位法REBCO高温超导涂层导体的成相机制和磁热相图研究

REBaCuO(REBCO, RE=rare earths) thin films are fundamental materials, not only for the applications of weak electronics, but also for the power applications. In recent years, the rapid development of the secondary generation of high-Tc superconducting tapes based on the epitaxial REBCO thin films, requires urgently people to study the mechanism further and to explore new technologies. The ex-situ thin film technologies with the separated steps consisting of coating first and subsequent phase formation with chemical reactions, exhibit remarkable advantages compared with the conventional ones, and thus emerge as the main trend of industrial processing of high-Tc superconducting tapes. Aiming at the phase formation, grain orientation, and flux pinning etc. key issues of the above-mentioned ex-site techniques, the present program will study the phase compositions as well as the defect features for those REBCO thin films prepared by the modified metalorganic solution deposition, and reactive co-evaporation at lower processing temperatures and partial oxygen pressures. We will investigate into the superconducting phase formation and texture at higher processing temperatures and partial oxygen pressures, and then establish the phase diagram with respect to the composition, structure, temperature and gas pressure, respectively. With the artificial control of a number of heterogeneous phases and related defects, one may expect the effective enhancement on the density of flux pinning centers, and then the improvement of superconducting carrying capacities in the magnetic fields. These researches are believed to be very significant and valuable, not only for fundamental theories, but also for the practical applications.

REBaCuO(REBCO, RE=稀土元素)薄膜是高温超导弱电和强电应用的基础材料，近年来高温超导涂层导体的快速发展，急需人们对REBCO薄膜的成材技术、外延织构和磁通钉扎等开展深入的研究。金属有机溶液沉积和反应共蒸发等先涂覆、后成相的异步法工艺在成材速率和性价比等方面比传统薄膜技术有显著的优势，正逐步成为第二代高温超导带材产业化的主流技术。本项目瞄准成相、织构和磁通钉扎等关键问题：研究异位法REBCO前驱薄膜组分的人工调控对低温、低氧下的物相和缺陷的影响；研究高温下超导相形成和外延织构的机制，特别关注其中由低维组分和结构（如纳米先驱颗粒和多层界面）诱导的非常规特性；确立与块体材料不同的组分-结构-工艺参数的相互关系；通过一系列电磁测量建立磁热相图，明确异质相密度对特征磁场及磁热相界线的调制作用，进而寻求提高磁场下临界电流密度的有效途径。这些研究既有基础理论的意义，又有很高的实用价值。

异位法REBCO薄膜的成相机制和磁热相图的研究对第二代高温超导带材的制备具有重要的指导意义。课题组开展了一系列高温超导体成材机理和电磁特性研究，特别是金属有机溶液法（MOD）、反应共蒸发（RCE）等异位法REBaCuO超导薄膜的外延生长、物相形成规律和电磁特性等研究。课题组完成了计划内容，取得的主要成果和创新点如下：（a）实现了高温超导薄膜及其涂层导体中的厚膜织构优化与致密化，明确带材吸氧过程中的氧行为、薄膜成核及外延生长特征等。(b)阐明了异位法YBaCuO超导薄膜的成相机制，特别是在纳米级前驱组分、应力调制下的物相关系及其对织构和电磁性能影响等。（c）发展了特色性的生长控制性技术，建立了新型的具有高度结构和成分无序的超导层。通过微结构和电磁特性观察测量，深入认识了磁通钉扎机制和各向异性特征等。（d）通过Eu、Hf、Zr等元素的掺杂产生有效的磁通钉扎中心，提高了超导薄膜的在场性能，随着外磁场的增加，掺杂样品表现出一个典型的从单磁通钉扎到集体钉扎，至磁通蠕动的过程。(e)通过有限元方法仿真，设计并数值计算了一款铁轭型高温超导磁体模型，明确了复合线径结构对磁体载流的优化作用。. 以上研究内容和成果针对了高温超导涂层导体涂层导体产业化和电力应用中的关键问题。加深了对MOD和RCE异位法REBCO薄膜的制备和物相形成规律的认识，在此基础上，提出了MOD和RCE工艺的改进和优化措施，获得了新工艺和组分。本课题的研究结果对高温超导薄膜的基础物性理解及其第二代高温超导带材的技术进步及电磁应用起到推动作用。已在国内外学术期刊发表相关学术论文38篇，其中 SCI 期刊论文27篇；获得相关发明专利授权6项；培养并毕业的博士生4名、硕士生16名。研究成果“第二代高温超导带材关键制备技术”获得2018年度上海市科技进步奖（发明二等奖）。