REBa₂Cu₃O_y (RE = Rare Earth: REBCO) coated conductors (CCs) fabricated by Trifluoroacetates Metal Organic Deposition (TFA-MOD) are expected to be used for magnet applications because of their low cost and high critical current density (J_c) in magnetic field. However, further improvement of the J_c in magnetic field is required for practical magnet applications. We have improved the J_c of TFA-MOD (Y_0.77Gd_0.23)Ba₂Cu₃O_y((Y,Gd)BCO) by introducing various BaMO₃ (BMO: M = Sn, Zr, Hf) nanoparticles [1-3]. To be effective, the BMO nanoparticles size has to be tuned, and the density needs to be higher with little degradation of the matrix crystallinity, carrier density (n_H) and critical temperature (T_c) for greater enhancement.

In this work, in order to clarify the effect of the size and density of BMO nanoparticles on the superconducting properties for TFA-MOD (Y,Gd)BCO+12 vol.%BMO CCs, the (Y,Gd)BCO CCs with different sizes and densities of BMO nanoparticles were fabricated on metal substrates. The all of (Y,Gd)BCO CC with and without BMO nanoparticles show almost same T_c and n_H, indicating superconducting matrix remains as standard (Y,Gd)BCO CC. We got significant enhancement of the in-field J_c for (Y,Gd)BCO+12 vol.%BMO CC over a broad temperature and field-angle range due to higher density of BHO and good size of BHO to pin a vortex. The improvements are seen not only in J_c but also in the reduction of the effects of thermal fluctuations (flux creep). Detailed microstructural and superconducting properties for nanocomposite (Y,Gd)BCO+12 vol.%BMO CCs will be presented.

Acknowledgments:
This work at Seikei University was supported by JST-FOREST (Grant Number JPMJFR202G). A part of this work was supported by JSPS KAKENHI (18KK0414 and 20H02184), Promotion and Mutual Aid Corporation for private Schools of Japan (Science Research Promotion Fund).

Keywords: Critical Current, flux creep, MOD, Coated Conductor