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Irradiation
Published in David A. Cardwell, David C. Larbalestier, Aleksander I. Braginski, Handbook of Superconductivity, 2023
Almost every conceivable kind of radiation has been applied to high temperature superconducting materials, especially in the early stages following their discovery by Bednorz and Müller in 1986. It was soon shown that their properties degraded in most cases, a fact that was related to the displacement of oxygen atoms and the corresponding reduction of the transition temperature Tc. However, a few types of radiation, in particular fast neutrons, high energy protons and very high energy heavy ions were found to significantly improve the irreversible magnetic properties of these superconductors, although some changes of Tc still prevailed. This is related to the introduction of flux pinning centres (i.e. of extended defects with sizes comparable to the superconducting coherence length) into the superconducting matrix and still represents the most successful way of improving the material performance with respect to the critical current densities Jc, the trapped magnetic fields in large bulk superconductors and the location of the irreversibility lines in the (H,T)-phase diagram.
Flux Pinning
Published in David A. Cardwell, David C. Larbalestier, I. Braginski Aleksander, Handbook of Superconductivity, 2023
Kees van der Beek, Peter H. Kes
Material imperfections providing flux pinning occur in many different varieties, and include inhomogeneities, defects, and engineered structures of sizes ranging from the atomic scale to the macroscopic scale. They are either naturally present as a result of the composition of the material, artificially introduced as the byproduct of the growth or preparation method, or tailored by micro- or nano-engineering. It is safe to assume that any imperfection of the material will lead to some extent of flux pinning and therefore affect the macroscopic physical properties of the superconductor, even if the effects may be very small. However, for the vast majority of superconducting materials, including technological superconductors, flux pinning will completely determine the electrical transport and magnetic properties in the superconducting state. One may classify flux pinning defects through the origin of the interaction with the vortex lines, through their “strength”, and through their shape: a cylindrical defect extending along the length of a vortex line will generally be more effective in arresting it than a point-like imperfection.
Superconductivity and superconducting materials
Published in David Jiles, Introduction to the Electronic Properties of Materials, 2017
The main objective of this chapter is to give an overview of superconductivity which includes a description of the basic observations of the phenomenon and an indication of the principal applications. We discuss the emergence of superconductivity in certain materials and how these materials are used in four main groups of applications: superconducting solenoids, superconducting magnetometers (SQUIDs), superconducting logic devices and superconducting power electronics devices. Both flux pinning by a superconductor and the Meissner effect are explained, together with the differences between Type i and Type ii superconductors. The onset of superconductivity is discussed as a discontinuous reduction in conductivity to a state with zero dc resistance. It is shown that the resistanceless state is insufficient to explain the Meissner effect in which magnetic flux is completely excluded from the bulk of a superconducting material. Conditions for establishing the presence of superconductivity are given.
Influence of chemical doping on flux pinning of GdBa2Cu3O7−z films
Published in Surface Engineering, 2018
L. Liu, W. T. Wang, B. L. Huo, M. J. Wang, Z. Yu, X. Yang, Y. Zhang, C. H. Cheng, Y. Zhao
The enhancement of Jc–B properties suggests that flux pinning centres have been introduced into the superconducting matrix by these two types of doping manners. Locally suppressed superconductivity by dilute Co doping and nanosized particles via BZO addition may act as the effective flux pinning centres. With a combination, it can be concluded that the improvement of surface microstructures and the formation of nanosized defects matching with the coherence length of GdBCO work together to enhance the current transport properties of the doped GdBCO films.
Influence of Y2Cu2O5 nanoparticles doping on superconducting properties of YBa2Cu3O7-δ
Published in Phase Transitions, 2019
Chemical doping of high-temperature superconductors (HTSC) by additive or substituent has been a routine way to alter the superconductor’s properties. YBa2Cu3O7-δ (YBCO) has been a superconductor which can be synthesized in a large scale easily and purely and has a crucial role in developing of superconducting wires and tapes so could be a suitable superconductor for industrial applications. Low critical current density of HTSC in the magnetic fields has been a serious HTSCs problem so the enhancement of critical current density has been one of the challenging issues for researchers in this area. The small coherence length, granular feature, weak links at grain boundaries and the weak flux pinning strength have been the most important restricting factors in reducing the critical current of HTSCs [1]. Although many ways have been proposed and solved, some problems like melt process fabrication which can reduce the weak links at grain boundaries [2], but it seems finding new ways to solve the problem of enhancing the critical current density in HTSCs is necessary. The critical current Jc is sensitive to the microstructure of HTSCs and by increasing the magnetic flux pinning centers increased [3], so by introducing nanoscale size of non-superconducting dopant into the superconducting grains, one can improve the Jc of HTSCs. At the beginning of the superconducting researches, it had been shown that by doping of YBCO superconductor by micrometer-sized Y2BaCuO5 (Y211) particles, the critical current could be somewhat improved [4] and the microcracks reduced [5]. So it was a creative impression to increase the Jc of HTSCs by doping them with nanoparticles in the range of coherence length of HTSCs [6]. By rapid development of science in the synthesis of different kinds of the nanomaterials, one can dope the superconductors by nanomaterials to increase the number of flux pinning centers and hence the critical current density of HTSCs materials. Various nanoparticles have been successfully doped in superconductors via sintering process which caused significant enhancement in their critical current density [7,8].