Epitaxial growth of Ba 2 YNbO 6 films on biaxially-textured NiW substrates as a multifunctional single buffer layer for
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Epitaxial growth of Ba2YNbO6 films on biaxially-textured NiW substrates as a multifunctional single buffer layer for high Jc epitaxial YBCO film Sung Hun Wee, and Claudia Cantoni, Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA Amit Goyal, Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; Departments of Chemical Biological Engineering, Physics, and Electrical Engineering, SUNY, University at Buffalo, Buffalo, NY 14260, USA Address all correspondence to Sung Hun Wee at [email protected] (Received 13 July 2015; accepted 20 August 2015)
Abstract Epitaxial Ba2YNbO6 (BYNO) films were deposited on textured NiW substrates via pulsed laser deposition. The films have dense and smooth surface structure, and more importantly, significantly improved out-of-plane texture, compared with the NiW substrate texture. Transmission electron microscopy study confirms the c-axis tilting of BYNO film and formation of misfit dislocations at NiW/BYNO interface, suggesting that the improved texture should be attributed to the tilted epitaxy via biased dislocation mechanism. YBa2Cu3O7−δ films deposited on BYNO single-buffered NiW substrates show further texture improvement, high superconducting transition temperature of ∼91 K, and critical current density of 1.8 MA/cm2 at 77 K, self-field.
Second generation (2G), high-temperature superconducting (HTS) wires or coated conductors are based on epitaxial growth of YBa2Cu3O7−δ (YBCO) films on biaxially-textured metallic substrates with multilayer buffers.[1] The purpose of the buffer layers is to provide a continuous, smooth, and chemically inert surface for epitaxial growth of YBCO films, while transferring the biaxial texture from the substrate to YBCO. Buffer layers typically consist of several functional layers that include: (i) a seed layer (e.g., Y2O3), a good epitaxial oxide layer on biaxially-textured NiW substrate without the formation of undesirable NiO and NiWO4 phases; (ii) a barrier layer (e.g., yttrium-stabilized ZrO2, YSZ) to provide an excellent chemical barrier to prevent diffusion of Ni from the NiW substrate to the YBCO layer; and (iii) a thin cap layer (e.g., CeO2) with latticematched with YBCO to provide chemical and structural compatibility with YBCO and to promote significantly cubeon-cube epitaxy of the YBCO layer.[1] Since each layer performs a single function, multiple buffer layers are typically required to fulfill all the required functions. However, it is desirable to combine two or more functionalities into one layer and thereby, reduce the number of the layers in terms of minimizing processing steps and cost-effective manufacturing for 2G-HTS wires.[2,3] Ba2RENbO6 (BRENO, RE = rare earth elements) are a group of ordered double perovskites with cubic or distorted cubic cells depending on RE3+ ionic radius.[4,5] Due to their excellent chemical inertness,[5,6] BRENO are reported as the promising substrate materials and buffer layers for YBCO film growth.[5–9] In add
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