Refinement of MgB2 grains and the improvement of flux pinning in MgB2 superconductor through nano-Ni addition
Refinement of MgB2 grains and the improvement of flux pinning in MgB2 superconductor through nano-Ni addition
复制标题
DOI：
10.1016/j.jallcom.2017.04.206
复制
发表时间：
2017-09
影响因子：
6.2
通讯作者：
Qian Zhao;C. Jiao;Enlong Zhu;Zheng Zhu
中科院分区：
文献类型：
--
作者：
Qian Zhao;C. Jiao;Enlong Zhu;Zheng Zhu
采用原位反应法制备了添加4at.%和6at.%Ni的多晶MgB2样品。用粗粉(40μm)和纳米粉(40 Nm)制备了块体样品。研究了烧结样品的相组成、微观结构和输运临界电流密度随镍颗粒尺寸的变化规律。较高的纳米镍加入量(6%)显著降低了镁和硼的反应温度，在固相阶段形成了缺陷较多、结晶度较差的细晶组织。结合差热分析(DTA)和扫描电子显微镜(SEM)分析发现，在506℃时，纳米镍粒子容易与镁形成镁镍共晶液体，从而在较低的温度下促进了镁B2的形成，改善了晶体的连通性。这种独特的微观结构使纳米Ni掺杂的MgB2块体超导体中的磁通钉扎得到了增强，其晶界更细小，晶界更多，夹杂物更多。而掺杂粗大的Ni颗粒，由于夹杂物的集中，钉扎作用较弱，从而使Jc显著降低，从而完全消除了Ni的积极作用。
Polycrystalline MgB2samples with 4 at.% and 6 at.% Ni addition were prepared by an in-situ reaction process. Coarse (40 μm) and nano-size (40 nm) Ni powders were used for synthesis of the bulk samples. The phase formation, microstructure, and transport critical current density of the sintered samples were investigated as a function of the Ni particles size. A higher amount of nano-Ni addition (6 at.%) was found to dramatically decrease the reaction temperature of Mg and B, forming MgB2fine grains with more defects and inferior crystallinity under the solid stage. Combined with the differential thermal analysis (DTA) and scanning electron microscopy (SEM) analysis, it was found that the nano-Ni particles is prone to form Mg-Ni eutectic liquid with Mg at 506 °C, which accelerates the formation of MgB2at a significantly lower temperature with improved grain connectivity. The unique microstructure, with refined MgB2grains, more grain boundaries and nano-inclusion inside matrix, is proposed to be responsible for the enhancement of flux pinning in the MgB2bulk superconductor with nano-Ni doping. However, the positive effect of Ni was completely eliminated by doping of coarse-Ni particle due to the concentration of the inclusions with weak pinning and thus a strong reduction ofJc.