Study of MgO-Based Buffer Layer Architecture for the Development of Ni–Cu-Based RABiTS YBCO Coated Conductor

摘要

MgO films are widely used as the first buffer layer in IBAD-YBCO coated conductors, whereas there are only a few examples of its use in RABiTS YBCO coated conductors. Nevertheless MgO, though challenging in terms of lattice parameter and epitaxy, can effectively passivate the metal substrate thus enabling the use of Ni–Cu-based alloy tapes. Such substrates develop a very sharp cube texture and at the same time can be safely handled when their thickness is as low as 40 $mu{rm m}$. Epitaxial MgO films were deposited by e-beam evaporation at 400 $^{circ}{rm C}$ on biaxially textured metal substrates. A transient Pd layer as thin as 10 nm was used to alleviate the lattice mismatch between MgO and the substrate and to enhance film adhesion. Due to the reduced diffusion of oxygen in MgO, this template is effective against substrate oxidation even in the extreme conditions typical of the YBCO growth. On such a template, ${rm La}_{0.66}{rm Sr}_{0.33}{rm MnO}_{3}$ (LSMO) was epitaxially deposited by PLD. Moreover, ${rm BaZrO}_{3}$ (BZO) film was successfully deposited by CSD on MgO single crystal and is expected to epitaxially grow also on MgO film.