${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta }$ Films Grown on Faceted Sapphire Fiber

There have been great advancements in the 2nd generation (2G) high temperature superconductors (HTS) wires termed coated conductors (CCs). Nevertheless, due to the high aspect ratio and the nature of metallic substrates, AC loss is a serious problem for the coated conductors. In this paper, we present a novel approach of fabrication of thin faceted sapphire fibers as substrates for YBCO film growth by laser heated pedestal growth (LHPG) technology. Single crystal sapphire fibers of about 100 μm in diameter with two r-plane facets on the sides have been successfully grown. By adjusting seed orientation and process optimization, the growth was tuned to the a-axis growth with extremely smooth r-plane on the sides. A buffer layer of about 30 nm was then deposited by magnetron sputtering followed by the superconductor layer of YBCO film. A critical current density over 1 MA/cm² has been demonstrated at 77 K self-field. Experimental results shows that fiber orientation and surface smoothness are critical for the performance of YBCO films and that can be achieved by the technologies presented.