Thick (2µm) epitaxial YBa2Cu3O7 films, on SrTiO3 substrates, were prepared at reaction temperatures of 725, 750 or 800C by using the BaF2 process. The direct-current critical current densities of the films were found to vary by a factor of 2 at 77K in perpendicular direct-current magnetic fields of up to 1.5T. The twin boundary spacing was essentially unchanged among these films while the size of the Y2O3 precipitates in the films varied by a factor of about 5. The measured a/b ratios of the films were markedly larger than those found in standard fully-oxygenated material. This appeared to be caused by the presence of the Y2O3 precipitates, which provided a strain constraint which limited the full tetragonal-to-orthorhombic phase transformation due to oxygenation.

Twin Boundaries and Critical Current Densities of YBa2Cu3O7 Thick Films Fabricated by the BaF2 Process. L.Wu, S.V.Solovyov, H.J.Wiesmann, D.O.Welch, M.Suenaga: Superconductor Science and Technology, 2003, 16[10], 1127-33