Epitaxial Growth of Y2O3 Buffer Films on Biaxially Textured Ni-W Tapes via a Photochemical Method

Buffer layers are indispensable components for YBa2Cu3O7−δ(YBCO)-coated conductors deposited on biaxially textured Ni-W metallic substrates, which act as diffusion barrier and epitaxial growth templates for superconducting films. In this work, both the Y2O3 single buffer film and the subsequent YBCO superconductor film were successfully fabricated on cube-textured Ni-W tapes via a facile photochemical-assisted sol–gel method. Specifically, the precursor gel films of Y2O3 were pretreated by ultraviolet (UV) irradiation. High-energy UV photons break organic chemical bonds and generate ozone and active oxygen radicals, which effectively decompose organic components and eliminate residual carbon at a low temperature. This photochemical treatment suppresses pore defects caused by the violent volatilization of organic substances during high-temperature annealing. The UV-treated Y2O3 buffer films present fine uniform grains and a low surface roughness of 5.46 nm, possessing excellent biaxial texture. The single-layer Y2O3 buffer can perfectly inherit the texture characteristics of the Ni-W substrate and provide a high-quality epitaxial growth template. On this sol–gel-derived Y2O3 buffer layer, the sol–gel-prepared YBCO superconducting film achieves high-quality in-plane epitaxial growth. The optimized YBCO-coated conductor exhibits a self-field critical current density of 2.65 MA/cm2 at 77 K with a superconducting transition width of 2.0 K, which confirms excellent superconducting performance. This vacuum-free photochemical-assisted sol–gel strategy provides a low-cost and promising technical route for the fabrication of high-quality single-buffer-layer YBCO-coated conductors.