Optimization of superconducting properties of the stoichiometric CaKFe4As4

Journal article

CaKFe4As4 (1144) is a unique stoichiometric iron-based superconductor which harbours high upper critical fields and large critical current densities. In this work, we describe a study to optimize the synthesis conditions of stoichiometric polycrystalline samples of CaKFe4As4 and asses their structural, magnetic and transport properties. The samples were prepared over a wide temperature range (900-1100°C) and the pure phase formation is centered around 955°C. Outside this temperature region, impurity phases of KFe2As2 and CaFe2As2 can also form. Magnetic susceptibility and resistivity measurements establish that the critical temperature reaches ~34 K for the optimum synthesis conditions and the critical current reaches 2 × 104 A-cm−2. The post-annealing process demonstrates the stability of the 1144 phase up to 500°C, however, under higher temperature annealing, phase degradation occurs. Our study indicates that the formation of phase-pure 1144 occurs over a much narrower window and its highly prone to multi-phase formation as compared with the 122 family. As a result, the superconducting properties are enhanced for the pure 1144 phase but they are likely to be affected by the inter and intra-granular behaviour originating from the microstructural nature of polycrystalline CaKFe4As4, similar to other iron-based superconductors. Based on our study, we construct the phase diagram for polycrystalline 1144 and compared it with that reported for 1144 single crystal.

Authors: Singh, S; Cassidy, S; Bristow, M; Blundell, S; Clarke, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: IOP Press
• Journal: Superconductor Science and Technology
• Volume: 33
• Issue: 2
• Article number: 025003
• Publication date: 2019-12-20
• Acceptance date: 2019-11-18
• DOI: 10.1088/1361-6668/ab58be
• EISSN: 1361-6668
• ISSN: 0953-2048