Biaxially Textured IBAD-MgO Templates for YBCO-Coated Conductors
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Biaxially Textured IBAD-MgO Templates for YBCO-Coated Conductors
Paul N. Arendt and Stephen R. Foltyn Abstract This article reports on the development of second-generation Y1Ba2Cu3O7– (YBCO)-coated conductors deposited on biaxially textured MgO templates fabricated using ion-beam-assisted deposition (IBAD). The materials system architecture and processing techniques used to achieve high critical supercurrents on flexible superalloy substrates is described. The texturing of YBCO films on metal substrates approaches that of films deposited on single-crystal oxide substrates. Critical currents and critical current densities of YBCO films on metal substrates are also equivalent to YBCO films deposited on single-crystal oxides. Keywords: biaxially textured MgO templates, high-temperature superconductors, IBAD, ion-beam-assisted deposition, YBCO.
Introduction In the area of second-generation hightemperature superconductor (HTS) wires, there are vigorous programs that have been undertaken by various institutions and consortia to develop long lengths of highquality superconducting tape using costefficient manufacturing techniques. The methodologies employed include diverse processes used to fabricate YBa2Cu3O7– (YBCO) HTS films as well as the biaxially textured template platforms on which the superconducting films are deposited. Ion-beam-assisted deposition (IBAD) of cubic metal oxide films is one of the approaches being pursued to form such textured templates. Within the IBAD research community, there have been many different cubic metal and metal oxide materials that have been demonstrated to be biaxially textured to some degree. Two of these that are currently being used as templates for long-length coated conductors are yttrium-stabilized zirconia (YSZ) and gadolinium zirconate (GZO). These are
MRS BULLETIN/AUGUST 2004
described in the article by Iijima et al. in this issue. A third template, magnesia (MgO), is the focus of this article. Before discussing IBAD-MgO and its specific advantages and disadvantages relative to the other IBAD templates, it is useful to briefly review the history of ion-beam processing methods employed to texture films.
Early History of Ion-Beam Texturing Experimental studies of the penetration of medium-energy ions (15–75 keV) in single crystals of fcc metals (Au and Al) found that the ion-penetration ranges decrease sequentially along the [110], [100], and [111] crystallographic directions, respectively.1–3 Computer simulations using Born–Mayer potentials to describe the range variations with crystallographic orientation of 5 keV Cu atoms in fcc Cu single crystals corroborated the experimental penetration distributions observed for Au and Al.4 It was concluded that channeling processes along the principal axes of fcc
crystal lattices were responsible for the qualitative resemblance between the experimental and calculated penetration range results.2,3 Analyses were also performed for 1–10 keV Cu atoms incident on various crystallographic directions of fcc, diamond, and bcc lattices.5
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