Critical current density improvement in CSD-grown high-entropy REBa 2 Cu 3 O 7- δ films.

High-entropy oxide (HEO) superconductors have been developed since very recently. Different superconductors can be produced in the form of a high-entropy compound, including REBa ₂ Cu ₃ O _{7- δ} (REBCO). However, until now, mainly bulk samples (mostly in polycrystalline form) have been reported. In this work, the first CSD-grown high-entropy (HE) REBCO nanocomposite films were successfully synthesized. In particular, high-quality Gd _0.2 Dy _0.2 Y _0.2 Ho _0.2 Er _0.2 Ba ₂ Cu ₃ O _{7- δ} nanocomposite films with 12 mol% BaHfO ₃ nanoparticles were grown on SrTiO ₃ substrates. The X-ray diffraction patterns show a near-perfect c -axis oriented grain growth. Both T _c and 77 K J ^sf _c , 91.9 K and 3.5 MA cm ^-2 , respectively, are comparable with the values of the single-RE REBCO films. Moreover, at low temperatures, specifically at 30 K, the J _c values are larger than those of the single-RE samples. A transmission electron microscopy (TEM) study, including energy-dispersive X-ray spectroscopy (EDXS) measurements, reveals that the different RE ³⁺ ions are distributed homogeneously in the matrix without forming clusters. This distribution causes point-like pinning centres that explain the superior performances of these samples at low temperatures. Although still seen as a proof-of-concept for the feasibility of preparing such films, these results demonstrate that the HE REBCO films are a promising option for the future fabrication of high-performance coated conductors. In the investigated B - T range, however, their J _c values are still lower than those of other, medium-entropy REBCO films, which shows that an optimization of the composition of the HE REBCO films is needed to maximize their performance.
Competing Interests: The authors declare no competing interests.
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