Determinant for self-organization of BaMO₃ nanorods included in vapor-phase-grown REBa₂Cu₃O_y films

BaMO₃ (BMO; M = Zr, Sn, and Hf) self-organizes into nanorod shape within REBCO films grown by vapor phase epitaxy. Controlling the number density of the BMO nanorods is effective for an improvement of critical current density of the REBCO films in magnetic fields. We focused on the growth mechanism of the BMO nanorods in this paper. BaHfO₃ (BHO) -doped REBCO films were fabricated under various conditions such as volume fraction of BHO and substrate temperature. We checked the number density and diameter of the BHO nanorods. We found that the volume fraction of BHO increased the number density, whereas the diameter was not affected by the volume fraction so much. The low substrate temperature contributed to the high number density in the films. Additionally, we carried out the 2-D Monte Carlo simulations for the nucleation and the self-organization of the BMO. The REBCO and BMO nuclei occurred randomly. However, due to small amount of BMO relative to REBCO, it was difficult for the BMO nuclei to get fat. We changed the molar fraction of the BMO and the substrate temperature in the simulations and evaluated the number density and the diameter of the resulting BMO nanorods.