Progress in Superconductivity and Cryogenics (한국초전도ㆍ저온공학회논문지)

The Korean Society of Superconductivity and Cryogenics (한국초전도저온학회)
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Germanium-based pinning dopants for MgB2 bulk superconductors

  • Chung, K.C. (Korea Institute of Materials Science) ;
  • Ranot, M. (Korea Institute of Materials Science) ;
  • Shinde, K.P. (Korea Institute of Materials Science) ;
  • Oh, Y.S. (Korea Institute of Materials Science) ;
  • Kang, S.H. (Korea Institute of Materials Science) ;
  • Jang, S.H. (Kiswire Advanced Technology Ltd) ;
  • Hwang, D.Y. (Kiswire Advanced Technology Ltd)
  • Received : 2019.05.31
  • Accepted : 2019.06.21
  • Published : 2019.06.30
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Abstract

Effects of the spherically shaped Ge and the rod-like carbon-coated Ge on the superconducting properties of $MgB_2$ were investigated. Pure Ge and carbon-coated Ge nano-powders were synthesized under the different amount of $CH_4$ (0 to 5 kPa) by using DC thermal plasma method. When the $CH_4$ was added ~100 nm sized Ge with a spherical shape changed to rod-like morphology with a diameter of ~30-70 nm and a length of ~400-500 nm. Also it was confirmed that thin carbon layers of a few nanometers were formed along the rod length and the agglomerated carbons were found on the edges of rods. Pure spherical Ge and Ge/C rods were mixed and milled with Mg & B precursor to form the doped $MgB_2$ bulk samples by the solid-state reaction method. Almost no change of $T_c$ was noticed for the pure Ge-added $MgB_2$, whereas $T_c$ was found to decrease with the Ge/C-added $MgB_2$ samples. It was found that the pure spherical Ge showed to have a negative effect on the flux pinning of $MgB_2$. However, Ge/C rods can enhance the flux pinning property of $J_c$ due to the coated carbon on Ge rods.

Keywords

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Fig. 1. FE-SEM images of (a) pure Ge nano-powder and Ge/C nano-composite at CH4 partial pressure of (b) 1 kPa, (c) 3 kPa, and (d) 5 kPa.

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Fig. 2. XRD data for pure Ge nano-powder and Ge/C nano-composite at different CH4 partial pressure.

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Fig. 3, XRD data of MgB2 doped with pure Ge & Ge/C composites and reference pure MgB2.

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Fig. 5. FE-SEM images of MgB2 bulk samples of pure and doped with pure Ge & Ge/C composites.

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Fig. 6. Critical current density vs. applied field of MgB2 bulk samples of pure and doped with pure Ge & Ge/C composites.

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Fig. 4. Analysis of MgB2 phase with angle shift of (002) and (110) reflections.

TABLE I ELEMENT ANALYSIS OF GE NANO-POWDER AND GE/C NANO-COMPOSITE AT DIFFERENT CH4 PARTIAL PRESSURE.

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