Effect of the sintering temperature on the microstructure and superconducting properties of MgB 2 bulks manufactured by the field assisted sintering technique
Effect of the sintering temperature on the microstructure and superconducting properties of MgB 2 bulks manufactured by the field assisted sintering technique
复制标题
烧结温度对场辅助烧结MgB 2 块体微观结构和超导性能的影响
DOI：
10.1088/1361-6668/ab7c53
复制
发表时间：
2020
影响因子：
3.6
通讯作者：
Matthews G
中科院分区：
文献类型：
--
作者：
Matthews G
二硼化镁(MgB2)块体超导体具有比传统铁磁体捕获更大磁场的能力和39K的转变温度，使其在无低温系统中具有良好的应用前景，可作为永磁体使用。与铜酸盐高温超导体不同，在多晶样品中，晶界作为钉扎点而不是弱连接，表现出良好的载流能力。这使得材料能够使用标准的陶瓷加工方法进行加工，这些方法可扩展到大直径和大规模生产。块体超导体的最大俘获场与材料的临界电流密度(Jc)和样品的半径成比例关系。为了在高场下获得可能的最高Jc值，要求块体材料是完全致密的细晶材料，并可能具有纳米级的非超导杂质粒子分布，以进一步加强钉扎。场辅助烧结技术(FAST)是一种从传统的无压烧结难以实现的材料中快速获得致密陶瓷的方法。从制造的角度来看，快速热处理是有吸引力的，因为样品在高温下保持的总时间很短，从而限制了颗粒的粗化。本文系统地研究了加工温度对FAST法制备的MgB2块材的显微组织和超导性能的影响。我们的结论是，要获得具有足够高的电连接性以产生大磁矩的材料，需要高于1000摄氏度的加工温度。然而，在900℃处理的样品中，由于其更细小的尺度微结构和更多的晶格缺陷，其本征(晶内)Jc值较好。
Magnesium diboride (MgB 2) bulk superconductors may have practical applications as permanent magnets owing to their ability to trap larger fields than conventional ferromagnets and a transition temperature of 39 K that make them attractive for use in cryogen-free systems. Unlike the cuprate high temperature superconductors, grain boundaries in MgB 2 act as pinning sites not weak links, and so show good current carrying ability in polycrystalline samples. This enables the materials to be processed using standard ceramic processing methods which are scalable to large diameters and mass production. The maximum trapped field in bulk superconductors scales with the critical current density (J c) of the material as well as the radius of the sample. To obtain the highest possible J c values in MgB 2 at high fields requires the bulk materials to be fully dense but fine-grained material, and possibly with a nano-scale distribution of non-superconducting impurity particles to further enhance pinning. Field assisted sintering technology (FAST) is a rapid process for obtaining dense ceramics from materials like MgB 2 which are difficult to sinter with conventional pressure-less techniques. Rapid heat treatments are attractive both from a manufacturing point of view and because the total time that the sample is held at high temperature is short, limiting grain coarsening. In this paper, we report a systematic study of the influence of processing temperature on microstructure and superconducting properties of MgB 2 bulks manufactured using FAST. We conclude that processing temperatures above 1000 C are required to obtain materials that have sufficiently high electrical connectivity to generate large magnetic moments. However, the intrinsic (intragrain) J c values in MgB 2 are better in the samples processed at 900 C owing to their finer scale microstructures and the MgB 2 lattice being more defective.