Biaxially Textured IBAD-MgO Templates for YBCO-Coated Conductors

Abstract

IntroductionIn 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 YBa 2 Cu 3 O 7-␦ (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 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 TexturingExperimental 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 These calculations resulted in an ordering of the channeling range dependencies for the Cu atom penetrations as a function of direction and lattice type. For the three lattice types studied, this ordering is illustrated in Table I, with the range variations listed in order from highest to lowest for the three lowindex directions. Sputter experiments using Cu and Ag single crystals for 1-10-keV Ar ions impacting within a few degrees of the three low-index planes found that the sputter yields progress from lowest to highest for the [110], [100], and [111] directions, respectively. 6 These sputter yield versus crystalline orientation results agreed with the predicted range variations for the fcc lattices, in that the probability of atoms being sputtered from a material is greater if the collisions between the incident ions and the atoms of the solid occur nearer to it...

Progress in research and development for REBCO coated conductors by reactive co-evaporation

“…Amorphous layers of Al 2 O 3 and Y 2 O 3 were deposited on the surface of Hastelloy tape which was continuously electro-polished, and first textured buffer layer, MgO was deposited successively using IBAD technology and finally a LaMnO 3 (LMO) layer was deposited for the buffered substrate. We selected MgO as a first textured material because its excellent bi-axial texturing was verified [6] in a very thin film, and focused on the continuous fabrication of long length IBAD-MgO tape using the reel-to-reel process.…”

“…Crystal grains of REBCO superconductor could be bi-axially aligned due to the developments of RABiTS [1][2][3] and IBAD template technologies [4][5][6], and critical current density (J c ) was greatly improved as a result.…”

Investigation of Early Nucleation Events in Magnesium Oxide During Ion Beam Assisted Deposition

“…The ion beam assisted deposition (IBAD) technique has been used to develop biaxial texture in a number of metals, metal oxides and metal nitrides [1][2][3][4] . The process is an enabling method for the development of second generation high-temperature superconducting coated conductors 2 .…”

“…The process is an enabling method for the development of second generation high-temperature superconducting coated conductors 2 . Initially, IBAD yttria-stablized zirconia (YSZ) allowed researchers to deposit biaxially aligned template films for the subsequent deposition of heteroepitaxial thin films of YBa 2 Cu 3 O 7-δ (YBCO) on flexible metal substrates [5][6][7] .…”

Remarkable progress in fabricating RE123 coated conductors by IBAD/PLD technique at Fujikura

“…However, its production rate was still late: Ion-Beam-Assisted-Deposition (IBAD) process speed was 5 ~ 7 m / h and Pulsed-Laser-Deposition (PLD) process speed was 5 ~ 15 m / h at best. In the IBAD process, it was reported that MgO exhibited sharp in-plane texture at only several tens nm, though our conventional Gd 2 Zr 2 O 7 (GZO) needs great thickness of about 1 mm [4][5][6]. Hence, the change of the IBAD materials from GZO to MgO will make dramatically high throughput possible.…”