Critical current density improvement in CSD-grown high-entropy REBa2Cu3O7-δ films.

Abstract

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 REBa2Cu3O7-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 Gd0.2Dy0.2Y0.2Ho0.2Er0.2Ba2Cu3O7-δ nanocomposite films with 12 mol% BaHfO3 nanoparticles were grown on SrTiO3 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 RE3+ 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.