Investigation of Phase Relations and Reaction Pathways in Pnictide Superconductors

Florida State University, Tallahassee FL

Investigators

Abstract

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.