Dehydrogenation-induced crystal defects for significant enhancement of critical current density in polycrystalline H-dop
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Dehydrogenation-induced crystal defects for significant enhancement of critical current density in polycrystalline H-doped MgB2 Qi Cai1,*
, Xinyao Li1, Shukui Li1,2,3, Chuan He1, Xingwei Liu1, and Xinya Feng1
1
School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, China China National Key Laboratory of Science and Technology on Materials Under Shock and Impact, Beijing Institute of Technology, Beijing 100081, China 3 State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China 2
Received: 6 August 2020
ABSTRACT
Accepted: 9 November 2020
The present study discovers the significant enhancement of critical current density by the pinning of borohydride and crystal defects in the hydrogentreated MgB2 bulks. Based on the concept of gas doping, the nanosized borohydride Mg(BH4)2 is formed by synthesizing H-doped MgB2 bulks in an H2 atmosphere at 300 °C and 350 °C, and the critical current density was enhanced over the entire field. The H-doped MgB2 bulks are then experienced dehydrogenation at 300 °C and 350 °C, respectively, and the decomposition of Mg(BH4)2 induced nanosized pits on the surface of the MgB2 grains, leading to a further enhancement of critical current density, 1.5 9 104 A cm-2 at 20 K and 2.5 T, which is three times larger than that of the un-doped MgB2 sample, 4.8 9 103 A cm-2. The hydrogenation and dehydrogenation hardly changed the superconducting transition temperature or the pinning mechanism of the MgB2 samples. The enhancement of the critical current density is possibly attributed to the pinning effects of the crystal defects, and the reduction of MgO.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
1 Introduction Magnesium diboride (MgB2) possesses the highest superconducting transition temperature, 39 K, among the intermetallic compounds, which enables it to steadily serve at 20 K, as the superconducting magnet or coil [1]. So far, the MgB2 superconductors have exhibited the technique and cost advantages for
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https://doi.org/10.1007/s10854-020-04862-x
the application in the magnetic resonance imaging (MRI) systems, owing to its high current carrying capacity, low grain-boundary weak links, and low refrigeration cost [2]. However, the critical current density, Jc, of the MgB2 superconductor drops dramatically with the increasing magnetic field, H, leading to the inapplicability of the MgB2 at a high magnetic field. If the magnetic field is pinned inside
J Mater Sci: Mater Electron
the superconductors, the resultant pinning force may offset the Lorentz force, which forms as the current passes through, and the critical current density is expected to be significantly improved. This relies significantly on the introduced pinning centers, including second-phase particles, lattice defects, and substitution atoms; meanwhile, the size of these pinning centers should be comparable to the coherent length of MgB2, 3.7–12.8 nm a
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