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Flux pinning and microstructure of bulk MgB2 doped by diverse additives
Superconductor Science and Technology ( IF 3.6 ) Pub Date : 2020-07-24 , DOI: 10.1088/1361-6668/aba01c
M Jirsa 1 , M Rameš 1 , M Miryala 2 , P Svora 1 , J Duchoň 1 , O Molnrov 1 , S S Arvapalli 2 , M Murakami 2
Affiliation  

In bulk high-temperature superconductors, Ag is usually used as an additive improving mechanical performance. In MgB2 doped by Ag, silver reacts with Mg, forming Mg-Ag phases acting as a vortex pinning medium. In this work, we analyze electromagnetic and pinning properties of bulk MgB2 doped by 1 wt% MgB4, 4 wt% Ag, and 1 wt% Dy2O3, prepared in Shibaura Institute of Technology (SIT), Tokyo. In three compounds of MgxB2 + 4 wt% Ag with x= 1, 1.075, and 1.1, the effect of Mg excess was studied. Magnetic moment was measured by vibrating sample magnetometer (VSM). Pinning was studied in terms of a pinning diagram, i.e. the field dependence of the normalized pinning force density, Fn=F/Fmax. In all studied samples, peak of the Fn (b) dependence (b=B/Birr, Birr being the irreversibility field) was observed at around b=0.2, indicating a prevailing flux pinning at grain boundaries. A slight shift of the peak with decreasing temperature indicated a defect size distribution in the pinning landscape. Transmission electron microscopy (TEM) showed a granular structure of all samples composed of MgB2 grains of about 230 nm (average size), with an ensembles of small grains (22 nm in average) of Mg3Ag, MgAg, Ag, Dy2O3, and MgB4. While the large MgB2 grains control the main pinning mechanism, the small precipitates seem to determine details of the current flow through the grain boundaries.

中文翻译:

不同添加剂掺杂的块体 MgB2 的通量钉扎和微观结构

在块状高温超导体中,Ag 通常用作提高机械性能的添加剂。在 Ag 掺杂的 MgB2 中,银与 Mg 反应,形成 Mg-Ag 相作为涡旋钉扎介质。在这项工作中,我们分析了在东京芝浦技术学院 (SIT) 制备的由 1 wt% MgB4、4 wt% Ag 和 1 wt% Dy2O3 掺杂的块状 MgB2 的电磁和钉扎特性。在 x=1、1.075 和 1.1 的 MgxB2 + 4 wt% Ag 的三种化合物中,研究了 Mg 过量的影响。通过振动样品磁强计(VSM)测量磁矩。根据钉扎图研究钉扎,即归一化钉扎力密度的场相关性,Fn=F/Fmax。在所有研究的样品中,在 b=0.2 附近观察到 Fn (b) 依赖性的峰值(b=B/Birr,Birr 是不可逆场),表明主要的通量钉扎在晶界。随着温度的降低,峰的轻微偏移表明钉扎图中的缺陷尺寸分布。透射电子显微镜 (TEM) 显示所有样品的颗粒结构由约 230 nm(平均尺寸)的 MgB2 晶粒组成,具有 Mg3Ag、MgAg、Ag、Dy2O3 和 MgB4 的小晶粒(平均 22 nm)的集合。虽然大的 MgB2 晶粒控制着主要的钉扎机制,但小的析出物似乎决定了通过晶界的电流的细节。具有 Mg3Ag、MgAg、Ag、Dy2O3 和 MgB4 小晶粒(平均 22 nm)的集合。虽然大的 MgB2 晶粒控制着主要的钉扎机制,但小的析出物似乎决定了通过晶界的电流的细节。具有 Mg3Ag、MgAg、Ag、Dy2O3 和 MgB4 小晶粒(平均 22 nm)的集合。虽然大的 MgB2 晶粒控制着主要的钉扎机制,但小的析出物似乎决定了通过晶界的电流的细节。
更新日期:2020-07-24
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