Enhancement of critical current density in MgB2 bulks burying sintered with commercial MgB2 powder

Cai, Qi; Liu, Yongchang; Xiong, Jie; Ma, Zongqing

doi:10.1007/s10854-018-9088-y

Cited by 3 publications

(1 citation statement)

References 19 publications

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“…Refinement of MgB 2 grains has been extensively studied with various methods, including the use of fine boron powder [46], mechanical refinement by milling [47][48][49][50], low-temperature heat processing [51][52][53][54][55], and impurity doping with Ni [56], Cu [57][58][59][60], Ag [61,62], In [63], and Hf [64]. Ma et al reported that lamellar MgB 2 grains can be formed with Mg-Cu liquid, and these lamellar MgB 2 grains are much better connected than the MgB 2 grains of typical morphology [60].…”

Section: Gb Engineering Of Mgbmentioning

confidence: 99%

Grain boundary characteristics of Fe-based superconductors

Iida

Hänisch

Yamamoto

2020

Supercond. Sci. Technol.

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the distance between strained regions is smaller or only slightly larger than the value of ξ within the GB plane, the superconducting order parameter is depressed at the GB and, hence, the super-current flow is impeded. Additionally, bending of the electronic bands at GBs deplete the charge carrier density 3 , which seriously decreases the superconducting transition temperature T c . Hence, to achieve large J c for cuprates, the crystallites should not only be aligned out-of-plane because J c is anisotropic but also be aligned in-plane within the misorientation angle θ GB , where the distance between strained regions is larger than ξ ab (ξ ab : in-plane coherence length) is satisfied. On the other hand, for LTS and MgB 2 with large coherence length (e.g. 5∼6 nm) and s-wave symmetry (for MgB 2 anisotropic swave), GBs are able to pin vortices in the mixed state, and especially also GBs with rather large angles. Therefore, increasing the GB densities by reducing the grain size usually leads to improved in-field J c properties.As stated above, the symmetry of superconducting order parameter and the coherence length mainly govern the J c characteristics at GBs for a given superconductor. Hence, for both LTS and HTS, understanding the nature of GB characteristics in combination with modifying the processing conditions, so-called GB engineering, is of great importance for reducing and/or controlling the defect density to tune the superconducting properties.The Fe-based superconductors (FBS) have similar physical properties as the cuprates, for instance a short coherence length due to the small carrier concentration and a low Fermi velocity 4 . Hence, FBS also seem to share the same GB issues as the cuprates. However, J c across GBs in FBS is not as severely reduced due to several features, which is reviewed in this article. Many reviews of the synthesis of FBS in the form of bulk samples and thin films, and of their physical properties have been published to date. Additionally, excellent review articles concerning bicrystals and GBs in cuprates have already been published 3,5,6 , however, only a few on GB issues for FBS have been published (e.g. 7 and 8). Grant Number 16H04646 as well as JST CREST Grant Number JPMJCR18J4. REFERENCES 1 Tomimoto K, Terasaki I, Rykov A I, Miura T and Tajima S, 1999 Phys. Rev. B 60 114 2 Tsuei C C and Kirtley J R 2000 Rev. Mod. Phys. 72 969 3 Hilgenkamp H and Mannhart J 2002 Rev. Mod. Phys. 74 485

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