It was recalled that there was a direct relationship between the critical current density and the grain-boundary angle in polycrystalline Cu3Ba2YO7 films. Grain boundaries with a mismatch angle greater than 5° usually resulted in reduced critical current densities. This detrimental effect of large-angle grain boundaries was attributed to strain fields that resulted from these grain boundaries. The quality of the Cu3Ba2YO7 film could be enhanced by straining the lattice in a specific direction. Direct experimental results were reported here which coupled, for the first time, local grain orientations and local strain maps for thin Cu3Ba2YO7 films that were deposited onto a (001) biaxially textured Ni substrate. It was shown that the grain structure of the Ni substrate affected the grain structure of the Cu3Ba2YO7 films; even in the presence of several buffer layers. The results also showed that high-quality films with high critical current densities could be produced, in spite of the presence of large-angle grain boundaries, if the film was compressed by some 0.5% strain normal to the a-axis.

Effect of Grain Orientation and Local Strain on the Quality of Polycrystalline YBa2Cu3O7 Superconductive Films. M.Amer: Philosophical Magazine Letters, 2002, 82[4], 241-5