论文标题
BI-2223超导体中不同固定机制的共存及其对将材料用于高电流应用的影响
Coexistence of different pinning mechanisms in Bi-2223 superconductor and its implications for using the material for high current applications
论文作者
论文摘要
我们研究了在高电流应用中使用的BI-2223（BI2SR2CA2CU3O10）的高临界电流多晶样品中的固定机制。使用差分磁光（DMO）成像技术，我们跟踪样品中的磁场穿透。我们的DMO成像研究显示，圆形区域的平均直径为20 UM，深色对比。我们将其识别为具有局部穿透场的强度固定区域，而周围地区则比周围地区更高。这些强度固定中心的一个独特特征是它们可以生存至高温（接近TC），并产生渗透场强度的非高斯分布。通过分析固定力行为的场依赖性，我们确定了两种不同的固定机制：在低温下，远低于TC，它主要是表面固定机制，在TC附近的较高温度下，我们看到了纯粹的Deltc固定机制。我们的研究表明，表面固定效应与样品中的晶粒比对，晶界和空隙有关。 TC附近的这些减小以及此处的强定位区域的影响与局部化学计量的波动有关。我们研究了这些固定中心对宏观BI-2223超导圆柱管中电流分布的影响。我们使用分布在圆柱体周围的霍尔传感器阵列来绘制跨宏观圆柱管的电流分布。该地图表明，在高电流下，电流分布在整个管子上都不均匀。非均匀性揭示了用于应用的超导体中大长度尺度上强定量中心的不均匀分布。
We investigate the pinning mechanism in high-critical-current polycrystalline samples of Bi-2223 (Bi2Sr2Ca2Cu3O10) utilized in high current applications. Using differential magneto-optical (DMO) imaging technique, we track the magnetic field penetration in the sample. Our DMO imaging studies show circular regions with an average diameter of 20 um with dark contrast. We identify these as strong-pinning regions with a substantially higher local penetration field than the surrounding regions. A unique feature of these strong-pinning centers is that they survive upto high temperatures (near Tc) and produce a non-Gaussian distribution of the penetration field strength. By analysing the field dependence of the pinning force behaviour, we identify two distinct pinning mechanisms: at low temperatures, well below Tc, it is predominantly surface pinning mechanism and at higher temperatures near Tc, we see a crossover into a purely delTc pinning mechanism. Our studies show that surface pinning effects are related to grain alignment, grain boundary, and voids in the sample. The effect of these diminishes near Tc, and the strong-pinning regions here are related to local stoichiometric fluctuations. We investigate the impact of these pinning centers on the current distribution in a macroscopic Bi-2223 superconducting cylindrical tube. We map the current distribution across the macroscopic cylindrical tube using an array of hall sensors distributed around the cylinder. The map shows that the current distribution is non-uniform across the tube at high currents. The non-uniformity reveals an inhomogeneous distribution of strong-pinning centers across large length scales in superconductors used for applications.
