Microstructures of REBa₂Cu₃O_7-y, films doped with artificial pinning center fabricated by vapor-liquid-solid method

In order to improve a critical current density under applied magnetic fields, an addition of BaMO₃ (BMO; M=Zr, Sn) nanorods into REBa ₂Cu₃O_y (REBCO) films is actively discussed. Although superconducting properties of the REBCO films are dramatically enhanced by self-assembled BMO nanorods, the growth mechanisms of the BMO nanorods have not been clarified yet. In this study, in order to clarify the growth mechanisms of the BZrO₃ (BZO) nanorods and to further improve the superconducting properties, we fabricated a BZO-doped Sm_1+xBa _2-xCu₃O_y (Sm + BZO) film by using modified Vapor-Liquid- Solid (VLS) technique (VLS-Sm + BZO/i). From the surface morphologies, there are BZO particles grown at step in the spiral growth measured by Br-etched VLS films doped with BZO. In general the impurity-related phase was pinning of growth fronts on REBCO films on substrate. Thus, we can conclude the variation of the surface morphology in VLS films is explained, not by the difference the step energy, but impurity phase could be responsible for the pinning and bending of different growth fronts, resulting in the formation of screw dislocations. From the plan-view TEM images, VLS-SmBCO + BZO film is approximately 9 nm in diameter of BZO nanorods, whereas VLS-SmBCO + BZO/i film is 7-8 nm. To create the BZO nano island/dots on the seed layer introduced the increase of the density of BZO nanorods. From the cross-sectional TEM images, columns of BZO nanorods aligned along [001] or the c-axis of SmBCO are clearly seen in the VLS films. Columnar BZO structures growing from the substrate to the surface have been observed. Nano BZO particles grown on the seed layer remained after the VLS growth. Nano BZO rods separated by 5 nm SmBCO spacer layers are shown to exhibit self-organized growth along c-axis of SmBCO.