Preparation of YBCO films by chemical vapor deposition in a magnetic field

YBCO films on single-crystalline MgO substrates and polycrystalline Ag substrates were prepared by chemical vapor deposition in magnetic fields up to 10 T, using a cryo-cooled superconducting magnet. In the case of the MgO substrates, microstructure was independent of the magnetic field but J_c was significantly improved. In contrast, with polycrystalline Ag substrates, the microstructure changed drastically; again J_c was improved. Large square-shaped grains with a size of 5-14 μm were observed for samples grown on Ag substrates at 0 T. These grains were reduced in size when a field of several tesla was applied during the CVD process and their shape became irregular above 4 T. These changes of the microstructure improve the critical current density. The values of J_c for the films deposited on the polycrystalline Ag substrates in 8 T were 5.76×10⁴ A/cm² at 0 T and 77.3 K.