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

熔融处理的单晶高温(RE)-BaCuO超导体，其中RE是一种稀土元素，如Nd，Sm，Eu，Gd或Y，由于其异常高的临界电流密度和高的不可逆场，被认为能够产生高磁场。因此，它们具有巨大的实际应用潜力，包括磁共振成像、磁悬浮、飞轮储能、电机和发电机。临界电流密度Jc是一个结构敏感参数，它与样品的微观结构密切相关。特别地，Jc与超导相单位体积内的钉扎中心数成正比。超导基质中尺寸较小(纳米级)的非超导相在(RE)BCO中形成了特别有效的磁通钉扎中心。通过插入纳米级的掺杂剂，JC可能会有显著的改善。(RE)BCO的掺杂包括两个特殊的挑战：第一个挑战是制备单晶形式的大块超导体，它实际上是单晶。单晶的优点是没有晶界，这会导致电阻和耗散，从而降低超导体中的电流量。标准(RE)BCO单晶的生长通常经历一个复杂的过程，包括包晶反应、晶种和缓慢冷却。纳米掺杂的引入可能会使单晶BCO的生长过程变得更加耗时和复杂。第二个挑战是研究超导基质中纳米颗粒或夹杂物的性质，包括通过成分分析区分颗粒类型，以克服传统能量色散X射线光谱分析(EDX)的限制。这将形成将纳米颗粒的分布与目标(RE)BCO材料中的局部JC相关联的基础。本PHD项目将致力于制备含纳米级掺杂的(RE)-BaCuO大块超导体的单晶。可以预见，(RE)-BaCuO的掺杂将改善其超导性能。除了用光学显微镜分析单颗粒样品的微观结构外，这个博士项目还将专注于利用扫描电子显微镜和其他先进的仪器技术对纳米相进行定量分析。该项目将把JC和上面确定的关键微结构特征联系起来，以使人们能够更深入地了解(RE)BCO单晶材料中的磁通钉扎。

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.