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Enhanced Critical Current Density in Bulk MgB 2

2018; IEEE Council on Superconductivity; Volume: 28; Issue: 4 Linguagem: Inglês

10.1109/tasc.2018.2793309

1558-2515

M. Muralidhar, Masaki Higuchi, Kotaro Kitamoto, M.R. Koblischka, M. Jirsa, M. Murakami,

Physics of Superconductivity and Magnetism

The object of this investigation is to improve the flux pinning and critical current density (J c ) of bulk MgB 2 materials for daily applications including superconducting permanent magnets. We prepared two sets of bulk MgB 2 materials employing commercial high-purity powders of Mg metal and carbon-coated amorphous B using a single-step solid-state reaction process. The first set of samples was produced by a single-step solid-state reaction at various temperatures between 794 °C and 806 °C in steps of 3 °C in pure argon atmosphere to optimize the sintering temperature. Further, the second set of samples was produced from Mg-rich MgB 2 material adding 1.5 wt% carbon-coated amorphous B powder to it, combined with 4 wt% of silver. X-ray diffraction analysis showed that samples were single-phase MgB 2 with minor trace of impurities. In all samples, sharp superconducting transition temperatures were observed around 38 K, which was decreased around 1 K in MgB 2 material produced with 1.5 wt% of carbon encapsulated boron. The critical current densities in Mg-rich MgB 2 material with 4 wt% of Ag were lower than in silver-free MgB 2 bulks. The sample with 1.5 wt% of carbon-coated B exhibited the highest J c of 460 kA/cm 2 at 20 K and self-field. Our results demonstrate a strong correlation between the microstructure achieved and the resulting pinning performance.