Large enhancement of the in-field critical current density of YBCO coated conductors due to composite pinning landscape

Abstract

YBa2Cu3O7-based coated conductors (CCs) achieve the highest critical current densities (J c) of any known superconductor and are a key technology for applications such as rotatory machines, high-field magnets and power transmission. Incorporation of nano-sized non-superconducting second phases as additional vortex pinning centers has been considered the most amenable route to further enhance J c at an industrial scale, and has been successfully used in commercial CCs. The resulting pinning landscape is quite complex, with both synergistic and competing interactions among the various types of defects. Particle irradiation, on the other hand, allows for a controlled post-processing incorporation of a well-defined defect morphology. We have previously shown that irradiation with protons and other light ions can further enhance the in-field J c in commercial state-of-the-art CCs. Here we develop a combined irradiation process that increases J c above values previously achieved by irradiating with only one species. Our new approach involves sequentially irradiating with 250 MeV Au ions and 4 MeV protons. For example, at T∼ 27 K (liquid neon) and µ 0 H∼ 4 T, a region of interest for rotatory machines applications, we obtain J c ∼ 5 MA cm−2, which is about 40% higher than the values produced by the individual irradiations. Finally, we conclude that this is due to the synergistic pinning effects of the introduced splayed, non-uniform columnar defects and small clusters.

In-situ measurements of the effect of radiation damage on the superconducting properties of coated conductors

“…These experiments show, except in low magnetic fields, that there is an initial improvement in J c with increasing irradiation dose, followed by a decrease in both J c and T c and eventual complete loss of superconductivity. Both the fluence at which the peak J c improvement is reached and the amount of any improvement are considered to be dependent on the sample temperature, type of projectile and the direction of the applied field [9][10][11][12]. For both ion and neutron irradiation, the degree of anisotropy in the superconducting properties of the textured REBCO in CC was also found to decrease with irradiation dose [10,[12][13][14][15].…”

“…Both the fluence at which the peak J c improvement is reached and the amount of any improvement are considered to be dependent on the sample temperature, type of projectile and the direction of the applied field [9][10][11][12]. For both ion and neutron irradiation, the degree of anisotropy in the superconducting properties of the textured REBCO in CC was also found to decrease with irradiation dose [10,[12][13][14][15].…”

Enhancement of self-field critical current density by several-tens-MeV ion irradiation in YBa2Cu3O7 films prepared by fluorine-free metal-organic deposition

“…large J c enhancement due to random 0D irradiation defects 12,13) and "dimpled" J c -versus-magnetic-field-angle curves 14,15) , suggesting a useful platform for reexamining the intrinsic properties of pins in YBCO films. In those studies using FF-MOD, J c sf was not enhanced, similarly to other deposition methods, 1,10,11) but irradiation defects had been introduced only for random 0D defects (ion energy E i < 5 MeV) but not for discontinuous/continuous 1D defects (E i > 20 MeV). In our present study, we observed significant enhancement (up to 63%) in J c sf in FF-MOD YBCO films at 77 K when discontinuous 1D irradiation defects were 5-10 nm in diameter, ∼20 nm in size along an ion track, had a ∼20 nm gap between defects in an ion track, and were directed in the caxis.…”

“…Indeed, it has been repeatedly reported that, in YBCO films, introduction of vortex-pinning centers (pins) by ion irradiation in the form of amorphous domains [3][4][5][6][7][8][9] causes an increase in J c only in applied magnetic fields but not in self-field. 1,10,11) Lack of a sufficient number of examples of "J c sf " enhancement in YBCO films makes it unclear what type of microstructure in the material is ideal for application (i) above, namely, for J c sf at high temperatures. 1,2) In this work, we performed 24-84 MeV Au-ion irradiation on 1 μm thick YBCO films prepared by fluorine-free metal organic deposition (FF-MOD) to gain insight into what type of microstructure in YBCO films is effective for J c sf at high temperatures.…”

Optimal Vortex Pinning in YBa2Cu3O7-x Superconducting Films Up to Very High Magnetic Fields

“…The presence of random point defects 37,38 also improved the ineld J c , especially at temperatures below 40 K. Secondary phase nanorods/nanocolumns 29,39,40 or irradiated columnar defects 26,31 enhanced J c mainly when H is parallel to the c-axis (H||c), especially at high magnetic elds and high temperatures; the same occured for natural defects such as twin boundaries 41,42 and dislocations 43,44 . Lately, hybrid nanostructures combining various defects [45][46][47][48][49][50] have also been investigated, with the aim of merging gains. However, only a few studies cover large magnetic eld and temperature ranges 6,51−53 .…”