Optimization of superconducting properties of the stoichiometric CaKFe4As4
Abstract
CaKFe4As4 (1144) is a unique stoichiometric iron-based superconductor which harbors 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 assess their structural, magnetic and transport properties. The samples were prepared over a wide temperature range (900 °C-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 behavior 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.
- Publication:
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Superconductor Science Technology
- Pub Date:
- January 2020
- DOI:
- 10.1088/1361-6668/ab58be
- Bibcode:
- 2020SuScT..33b5003S
- Keywords:
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- iron based superconductors;
- transition temperature;
- critical current density;
- granular superconductors