石井 涼太

Abstract We fabricated GdBa₂Cu₃O_7-δ (Gd123) superconducting thin films on LaAlO₃ single-crystal substrates using the FF-MOD method. The superconducting properties of thin films doped with various volume fractions of Gd₂CuO_4-x (Gd214) as new type of artificial pinning centers (APCs) were evaluated. As a result, we successfully introduced up to 5.95vol% of the c-axis oriented Gd214 into Gd123 films. The maximum J _C at 4.2 K was observed in the film doped with 1.98vol% Gd214, reaching 3.05 MA/cm² at 3.0 T and 2.00 MA/cm² at 6.9 T, which are 2.21 times and 2.75 times higher than those of the non-doped film, respectively. Building on these results, we attempted to introduce various types of RE ₂CuO_4-x (RE214: RE= Gd, Sm, Nd) microcrystals as APCs and investigated their superconducting properties. The findings revealed that lattice matching between the c-axis lattice constants of the base material and the pinning material is critical to improve J _C-B properties.

Abstract We have fabricated BaCeO₃ (BCO) and Gd₂CuO₄ (Gd214) co-doped GdBa₂Cu₃O_7-δ thin films on LaAlO₃ single crystal substrates by fluorine-free metal organic deposition method and investigated their crystallinity and superconducting properties. The J _C-B properties of the co-doped film were improved compared to those of films with single Gd214 or BCO doped films at the same volume fraction, respectively. 2vol% Gd214 and 1vol% BCO co-doped film showed the maximum J _C of 5.92 MA/cm² (4.2 K, B//c, B=1 T) and 0.24 MA/cm² (77.3 K, B//c, B=1 T). These values were 1.89 and 1.85 times higher than those of the 3vol% single Gd214 doped film, respectively.

Abstract We have synthesized middle-entropy type REBCO (ME-REBCO) and high-entropy type REBCO (HE-REBCO) superconducting thin films with BaCeO₃ artificial pins by fluorine-free metal organic deposition (FF-MOD) method and evaluated their crystallinity and superconducting properties. The c-axis orientation of crystals was confirmed by XRD analysis for all thin films. The superconducting transition temperatures in all films were over 90 K. STEM observation revealed that the crystal lattice of HE-REBCO was slightly distorted compared to a normal GdBCO film. This distortion is expected to be a “backlash” in the crystal and contribute to an increase in the allowable amounts of artificial pins. The critical current densities and flux pinning force densities at 77.3 K were enhanced by Ce doping, indicating that BaCeO₃ artificial pins were introduced into the FF-MOD ME-REBCO and HE-REBCO films.

Abstract We have fabricated GdBa₂Cu₃O_7-δ thin films co-doped several types of BaMO₃ (M=Zr, Sn, Ce) artificial pinning centers with different lattice constants and Young’s modulus from 2.0 to 5.0 mol% on LaAlO₃ single crystal substrates by the FF-MOD method. When several types of BaMO₃ are simultaneously introduced into Gd123 films by the FF-MOD method, Ba required for BaMO₃ crystal growth is shared among them, each crystal growth is suppressed, and thus the crystals become finer and denser. This resulted in a remarkable enhancement of the critical current densities in magnetic fields. The maximum J _c of 16.57 MA cm^-2 at 0 T and 1.97 MA cm^-2 at 3.0 T, 30 K obtained for the Gd123 film introduced three types of BaMO₃ (M=Zr, Sn, Ce) with 4.0 mol% were 1.22 and 1.76 times larger than those for the film with the same amount of BaCeO₃. This method shows a new strategy to improve J_c in magnetic fields of REBCO.