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

YBCO films on single-crystalline MgO substrates and polycrystalline Ag subs trates 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 su bstrates, microstructure was independent of the magnetic field but J(c) was significantly improved. In contrast, with polycrystalline Ag substrates, t he microstructure changed drastically; again J(c) was improved. Large squar e-shaped grains with a size of 5-14 mum were observed for samples grown on Ag substrates at 0T. These grains were reduced in size when a field of seve ral tesla was applied during the CVD process and their shape became irregul ar above 4T. These changes of the microstructure improve the critical curre nt density. The values of J(c) for the films deposited on the polycrystalli ne Ag substrates in 8 T were 5.76 x 10(4) A/cm(2) at 0 T and 77.3 K. (C) 20 01 Elsevier Science B.V. All rights reserved.