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Fig.1 The magnetic field characteristics of the critical current for the Sr-122 single core iron-based superconducting tape, 7-core and 19-core Sr-122 multicore iron-based superconducting tapes prepared by the new process. The critical current density of the developed Sr-122 single-core strip at 4.2K and 10 T reached the highest level of 105 A/cm2.
Recently, Ma Yanwei's research group of the Applied Superconducting Key Laboratory of the Institute of Electrical Engineering of the Chinese Academy of Sciences adopted a new mechanical pressing process to develop the world's highest transmission critical current density Sr122 iron-based superconducting tape strip, exceeding 105 A at 4.2K and 10T. /cm2 (Appl. Phys. Lett. 104 (2014) 202601), this achievement marks the country's entry into the practical threshold, and lays a solid foundation for China's next large-scale iron-based long-term preparation.
After researching and developing the world’s first iron-based superconducting wire in 2008, the research group has systematically studied a number of key technologies such as metal sheathing materials, machining and heat treatment processes, doping modification, and texture orientation. Improve the critical current density of iron-based superconducting tapes and always maintain its leading position in the international community.
After years of technical accumulation and continuous efforts, this group prepared high-quality precursor powders, and first introduced the hot-pressing process into the preparation of iron-based superconducting tapes, which significantly improved the density of superconducting cores and effectively eliminated them. The microcracks significantly increase the critical current density of Sr-122 iron-based superconducting tape to 5.1×104 A/cm2 (4.2K, 10T). This result was published in Scientific Reports 4, 4465 in March 2014 ( 2014) (DOI: 10.1038/srep04465).
Subsequently, by further optimizing the pressing process, the research team prepared a textured Sr-122 iron-based superconducting tape with a high density, and its transmission critical current exceeded the practical application of 105 A/cm2 (4.2 K, 10 T) for the first time. Level. High-resolution transmission electron microscopy studies of the grain boundary structure at the atomic scale have revealed that the grains in the superconducting tape core are tightly connected and there is no impurity phase between the grains, and a large number of small-angle grain boundaries are observed.
Therefore, the regulation of the microstructure of the material and the optimization of the high-quality superconducting phase make the iron-based superconducting tape obtain a high critical current density. Related work has been published recently in Appl. Phys. Lett. 104, 202601 (2014) (DOI: 10.1063/1.4879557), and has been highly reviewed by the reviewers: The ascetic JC reported in Sr122 tape is very encouraging for the superconductivity community .
In order to further promote the application of 122 iron-based superconducting tape strips, the group also prepared high-performance 7-core and 19-core multicore strips, of which the former had a critical current density of 6.1×104 A/cm 2 (4.2K, 10T). ), is the highest record of iron-based superconducting multicore lines.
On the other hand, the 1111 iron-based superconductor has a higher superconducting transition temperature and upper critical field than the 122 iron-based superconductor, but due to the high synthesis temperature of the 1111 iron-based superconductor, the uniformity and phase purity are not easy to control, so the line The preparation of the strip is also more difficult than the 122-strand strip.
Recently, the research group added tin to the sintering process of SmFeAsO1-xFx (Sm-1111) precursor powder, effectively eliminated the FeAs impurity phase between Sm-1111 grains, and increased the critical current density of Sm-1111 strip transport. Up to 3.45 x 104A/cm2 (4.2K, 0T), which is the highest reported value for the current 1111 iron-based superconducting tape strip. The paper was published in Appl. Phys. Lett. 104, 172601 (2014) (DOI: 10.1063/ 1.4874261).
The above work was supported by the "973" plan of the Ministry of Science and Technology, the National Natural Science Foundation of China, and the Beijing Science and Technology Commission.
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