In this study, REBCO thin films substituted RE sites with three or more elements with BMO3-type artificial pinning centers were fabricated by FF-MOD method, and their superconducting properties were evaluated. Mixing entropy ∆Sconf defined by ∆Sconf=R ln(n) (where R is the gas constant and n is the number of elements) increases as the number of elements at the RE site increases [1]. It is expected that the Gibbs free energy ΔG=ΔH-TΔS will decrease due to the increase in the mixing entropy, leading to stabilization of crystallinity. In such REBCO thin films, it is expected that larger volume fraction of BMO3-type artificial pinning centers can be introduced without deteriorating the crystallinity of the base superconducting material, compared to when RE is a single element, because the crystallinity is stabilized. When the mixing entropy is 1.5R or more, it is called high-entropy type superconductors [2]. As for REBCO thin films, we have also succeeded in fabricating high-entropy REBCO thin films by substituting RE sites with five elements, Gd, Sm, Nd, Eu, and Y, by the FF-MOD method [3]. When 1 mol% of Ce was added to this high-entropy REBCO thin film and BaCeO3 was introduced as an artificial pin, the critical current density JC at 30 K and 1 T increased 1.4 times that of non-doped high-entropy REBCO. In this study, we optimized the fabrication process to increase the amount of artificial pinning of high-entropy REBCO thin films and NdEuGd123 thin films with ternary RE elements to improve JC properties in magnetic fields.
[1] Jien-Wei Yeh, Swe-Kai Chen, Su-Jien Lin, Jon-Yiew Gan, TsungShune Chin, Tao-Tsung Shun, Chun-Huei Tsau, and Shou-Yi Chang, “ Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes ” , ADVANCED ENGINEERING MATERIALS 2004, 6, No. 5.
[2] P. Koželj, S. Vrtnik, A. Jelen, S. Jazbec, Z. Jagličić, S. Maiti, M. Feuerbacher, W. Steurer and J. Dolinšek, “Discovery of a Superconducting High-Entropy Alloy”, PHYSICAL REVIEW LETTERS, 113, 107001 (2014).
[3] H. Masuda, R. Ishii, R. Kita and O. Miura, “Superconducting Properties of High-Entropy Type RE123 Thin Films by Fluorine-Free MOD Method”, IEEE Transactions on Applied Superconductivity ( Volume: 33, Issue: 5, August 2023).
We gratefully acknowledge the work of past and present members of our laboratory and Professor Miura.