Growth and superconducting properties of (RE)Ba2Cu3O7-d single grain superconductors containing nano-size dopants

已知熔融处理的单晶粒高温（RE）-Ba-Cu-O超导体（其中RE是稀土元素，例如Nd、Sm、Eu、Gd或Y）由于其异常高的临界电流密度和其高的不可逆场而能够产生高磁场。因此，它们在一系列实际应用中具有巨大的潜力，包括MRI，磁悬浮，飞轮储能，电动机和发电机。临界电流密度Jc是一个结构敏感的参数，这是严重依赖于样品的微观结构。特别地，Jc与超导相中每单位体积的钉扎中心的数量成比例。超导基质中具有小尺寸（在纳米范围内）的非超导相在（RE）BCO中形成特别有效的磁通钉扎中心。通过插入纳米尺寸的掺杂剂，Jc可以潜在地显著提高。（RE）BCO的掺杂包括两个特殊的挑战：第一个挑战是以单个晶粒的形式制造块状超导体，其实际上是单晶。单一晶粒的优点是没有晶界，晶界导致电阻和耗散，因此降低了超导体中的电流量。标准（RE）BCO单晶的生长通常通过包括包埋反应、引晶和缓慢冷却的复杂过程。纳米尺寸掺杂剂的引入可能使单晶粒（RE）BCO的生长过程成为更加耗时和复杂的任务。第二个挑战是研究超导基质中纳米颗粒或夹杂物的性质，包括从克服传统能量色散X射线光谱（EDX）局限性的成分分析中区分颗粒类型。这将形成将纳米颗粒的分布与靶（RE）BCO材料中的局部Jc相关联的基础。这个博士项目将专注于制造含有纳米尺寸掺杂剂（如RE 2 O3）的（RE）-Ba-Cu-O块状超导体的单个晶粒。可以预见，（RE）-Ba-Cu-O的掺杂将改善其超导性能。除了使用光学显微镜分析单颗粒样品的微观结构外，该博士项目还将专注于使用扫描电子显微镜和其他先进的仪器技术定量分析纳米级相。该项目将关联Jc和上面确定的关键微观结构特征，以便更深入地了解（RE）BCO单颗粒材料中的磁通钉扎。

Melt processed, single grain high-temperature (RE)-Ba-Cu-O superconductors, where RE is a rare-earth element such as Nd, Sm, Eu, Gd or Y, are known to be able to generate high magnetic fields due to their unusually high critical current densities and their high irreversible fields. Therefore, they have significant potential for a range of practical applications, including MRI, maglev, flywheel energy storage, motors and generators. The critical current density Jc is a structure-sensitive parameter, which is dependent critically on the sample's microstructure. In particular, Jc is proportional to the number of pinning centres per unit volume in the superconducting phase. Non-superconducting phases with small dimensions (in the nanometer range) within the superconducting matrix form particularly effective flux pinning centres in (RE)BCO. By inserting nano-size dopants, Jc can potentially improve significantly. The doping of (RE)BCO includes two particular challenges: The first challenge is the fabrication of bulk superconductors in the form of a single grain, which is effectively a single crystal. The advantage of single grains is the absence of grain boundaries, which lead to resistance and dissipation and therefore lower the amount of current in the superconductor. Standard (RE)BCO single grains grow typically through a complicated process including a peritectic reaction, seeding and slow cooling. The introduction of nano-size dopants may make the growth process of single-grain (RE)BCO an even more time-consuming and complicated task. The second challenge is the investigation of the nature of the nano-sized particles, or inclusions in the superconducting matrix, including distinguishing the types of particles from composition analysis that overcome the limitations of conventional Energy-dispersive X-ray spectroscopy (EDX). This will form the basis of correlating the distribution of nanoparticles to local Jc in target (RE)BCO materials. This PhD project will focus on the fabrication of single grains of (RE)-Ba-Cu-O bulk superconductors containing nano-size dopants, such as RE2O3. It can be anticipated that doping of (RE)-Ba-Cu-O will improve its superconducting properties. In addition to analysing the microstructures of the single grain samples using optical microscopy, this PhD project will also focus on analysing the nano-sized phases quantitively using scanning electron microscopy and other advanced instrumental techniques. The project will correlate Jc and the key microstructural features identified above to enable a deeper understanding of flux pinning in (RE)BCO single grain materials.