Investigation of Phase Relations and Reaction Pathways in Pnictide Superconductors

非技术描述：2008年，一种新的含有铁和砷的高温超导体被发现。从那时起，人们对这些和相关的锂离子超导体(包括N、P或As)进行了一系列的研究，(操作的)临界温度已提高到55K。这些材料特别引起物理学界的兴趣，因为它们具有耐人寻味的磁性和超导性质的组合，它们对应用超导界具有重要意义，因为它们似乎具有超导性质，使它们适合于实际应用。然而，实际应用需要高质量的散装材料，具有干净、连接良好的晶界，允许超电流在材料中从一个颗粒移动到另一个颗粒。由于多相混合物通常含有覆盖晶界的Fe-As相，今天制造的块状磷灰石超导体严重限制了电流通过晶界的传输。技术细节：该项目的智力优势在于研究相关系和反应路径，以了解如何处理磷灰石超导体，以制造具有干净、连接良好的晶界的高质量块体材料。了解样品中应该存在什么相(相关系)和实际存在什么相(反应路径)，指导开发新的热处理方法来制备大块样品。由此得到的高质量样品可用于评估关键的整体性能，例如多晶样品中的临界电流密度。本工作研究了含有Ba(Fe1-xCox)2As2超导体的Ba-Fe-As-Co系统。这项研究的更广泛的影响是让学生和教师参与到对pNictide超导体的研究中，并让普通观众接触到超导的奇迹和超导加工的世界。具体地说，Hellstrom继续从代表性不足的群体中招收暑期学生，并在暑期与K-12教师合作。他还在扶轮社和其他地方民间组织发表关于超导电性的演讲。

NON-TECHNICAL DESCRIPTION: In 2008 a new family of high-temperature superconductors that contain Fe and As was discovered. There has been a flurry of work on these and related pnictide superconductors (containing N, P or As) since then and the critical temperature (for operation) has been raised to 55 K. These materials are particularly interesting to the physics community because they have an intriguing combination of magnetic and superconducting properties, and they are of significance to the applied superconductivity community because they appear to have superconducting properties that may make them suitable for practical applications. However, practical applications require high-quality bulk material with clean, well-connected grain boundaries that allow supercurrent to move from grain to grain across the material. The bulk pnictide superconductors made today suffer from severely limiting current transport across grain boundaries due to multiphase mixtures that typically contain a Fe-As phase that covers the grain boundaries.TECHNICAL DETAILS: The intellectual merit of this project lies in investigating phase relations and reaction pathways to understand how to process pnictide superconductors to make high-quality bulk material that has clean, well-connected grain boundaries. Knowing what phases should be present in a sample (phase relations) and what phases are actually present (reaction pathways) guides the development of new heat treatments to make bulk samples. The resulting high-quality samples can be used to evaluate key bulk properties such as the critical current density in polycrystalline samples. This work investigates the Ba-Fe-As- Co system, which contains the Ba(Fe1-xCox)2As2 superconductor. The broader impact of this research is to involve students and teachers in research on pnictide superconductors and expose lay audiences to the wonders of superconductivity and the world of superconductor processing. Specifically, Hellstrom continues to recruit summer students from underrepresented groups and to work with K-12 teachers during the summer. He also gives talks on superconductivity at the Rotary Club and other local civic organizations.