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Flux Pinning Enhancement in YBa2Cu3O7-x Films for Coated Conductor Applications (Postprint)
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
Pagination or Media Count:
It is shown that YBCO films with BaSnO3 BSO nano-additions, made with either a sectored target or with a premixed target using pulsed-laser deposition PLD, have a much greater improvement in Jc at the higher fields with an Hc orientation. More than two orders of magnitude improvement in Jc was observed as compared to undoped or similarly processed Y2BaCuO5 Y211 doped samples at magnetic fields higher than 5 T. The improvement was found to be due to the formation of BSO nanocolumns 8 10 nm in diameter in the films. These nanocolumns nucleate at the interface and subsequently grow perpendicular to the substrate while allowing high-quality YBCO to grow around them. Although similar processing conditions were used, Y211 formed nanoparticles, whereas BSO formed nanocolumns in the YBCO because of the crystal structure match between BSO and YBCO both are perovskites and appropriate lattice strain and suitable deposition conditions. The BSO content was also systematically increased from 2 to 20 mol by using premixed targets of YBCO and BSO to explore the effects of BSO content variation in YBCO. It was shown that even with 20 mol BSO addition films can be grown without a significant decrease in critical transition temperature Tc. While the diameter of the nanocolumns remained at 8 10 nm, the distance between them decreased from 50 nm to 20 nm as the concentration was increased from 2 mol to 20 mol, resulting in an increase in the number density. An overall improvement at both low and high fields was observed in samples of YBCO10 mol BSO. The YBCOBSO films deposited on buffered metallic substrates showed improvements as seen on the single-crystal substrates, indicating that the BSO nano-additions can be introduced on polycrystalline buffer layers as used in coated conductors. Unlike BaZrO3, BSO seems to allow higher relative amounts of additions to YBCO without significantly depressing the Tc value. The BSO nanocolumns seem to grow as solid nanorods.
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