Grain orientations and grain boundary networks of Yba_2Cu_3O_(7-delta) films deposited by metalorganic and pulsed laser deposition on biaxially textured Ni-W substrates

摘要

We report a detailed study of the grain orientations and grain boundary (GB) networks in Yba_2Cu_3O_(7-delta) (YBCO) films -0.8 mum thick grown by both the in situ pulsed laser deposition (PLD) process and the ex situ metalorganic deposition (MOD) process on rolling-assisted biaxially textured substrates (RABiTS). The PLD and MOD growth processes result in columnar and laminar YBCO grain structures, respectively. In the MOD-processed sample [full-width critical current density J_c(0 T, 77 K) = 3.4 MA/cm~2], electron back-scatter diffraction (EBSD) revealed an improvement in both the in-plane and out-of-plane alignment of the YBCO relative to the template that resulted in a significant reduction of the total grain boundary misorientation angles. A YBCO grain structure observed above individual template grains was strongly con-elated to larger out-of-plane tilts of the template grains. YBCO GBs meandered extensively about their corresponding template GBs and through the thickness of the film. In contrast, the PLD-processed film [full width J_c(0 T, 77 K) = 0.9 MA/cm~2] exhibited nearly perfect epitaxy, replicating the template grain orientations. No GB meandering was observed in the PLD-processed film with EBSD. Direct transport measurement of the intra-grain J_c(0 T, 77 K) values of PLD and MOD-processed films on RABiTS revealed values up to 4.5 and 5.1 MA/cm~2, respectively. As the intra-grain J_c values were similar, the significantly higher full-width J_c for the MOD-processed sample is believed to be due to the improved grain alignment and extensive GB meandering.