Processing dependence of texture, and critical properties of YBa ₂ Cu ₃ O _7-δ films on RABiTS substrates by a non-fluorine MOD method

YBa ₂Cu ₃O _7-δ (YBCO or Y123) films on rolling-assisted biaxially textured substrates (RABiTS) were prepared via a fluorine-free metallorganic deposition (MOD) through spin coating, burnout, and high temperature anneal. The effects of substrate texture and surface energy of the CeO ₂ cap layer were investigated. Except for the commonly accepted key factors, such as the textures of substrate and buffer layers, we found some other factors, for example, the deposition temperature of the cap layer, are also critical to the epitaxial growth of Y123 phase. With the CeO ₂ cap layer deposited at relative high temperature of 700°C, a critical current density, J _c, over 1 MA/cm ² has been demonstrated for the first time on Ni-RABiTS by a fluorine-free MOD method. Whereas for samples with CeO ₂ cap layers deposited at a lower temperature of 600°C, even though XRD data showed a better texture on these buffer layers, texture degradations of YBCO grains under the optimized processing conditions were observed and a lower oxygen partial pressure around 40 ppm was necessary for the epitaxial growth of Y123 phase. As a result, J _c fell to 0.45 MA/cm ² at 77 K. The observed phenomena points to the change of surface energy and reactivity of the CeO ₂ cap layer with respect to the CeO ₂ deposition temperature. In this paper, the YBCO phase diagram was also summarized.