Present status and perspective of IBAD and PLD system in SRL and self-epitaxy in PLD-CeO 2 on IBAD seed layer

Abstract

This paper reports the recent activity for the coated conductor in Superconductivity Research Laboratory (SRL), especially concerning to the ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD) methods, which are considered to be the most promising from the recent achievements in terms of the length and critical current density. In SRL, we have recently introduced a reel-to-reel IBAD machine. The IBAD machine successfully brought about a textured Gd 2Zr 2O 7 layer on Hastelloy tapes. The degree of in-plane texturing, delta phi Δ ϕ, of the samples was 13° in a meter long conductor. This IBAD machine will be a strong tool to study a long YBCO coated conductor. The second recent result is the PLD-CeO 2 buffer layer on an IBAD tape. Being different from the conventional studies, the PLD-CeO 2 layer not only grew epitaxially but also developed its degree of texturing during the PLD deposition. The degree of texturing in the CeO 2 layer reached in the order of 2° and 5° on the IBAD tapes with Δ ϕ around 10° and 25°, respectively. The texturing was so fast that we obtained a Δ ϕ of 10° in 1 min and 5–6° in 6 min, starting from a thin IBAD substrate with a Δ ϕ of 24–27°. We can call this “self-epitaxy” in the meaning of using no assist like Ar ion in the IBAD method. This new epitaxy phenomenon resulted in a small misorientation angles between grains and then reduced the weak-link induced degradation of J c in the grain boundaries of the conductor. A PLD-YBCO layer on the above CeO 2 layer achieved a critical current density as high as 3.8 MA/cm 2 at 77 K and 0 T, which was not so largely degraded compared to the conventional coated conductors with the misorientation angles around 10° and J cs of 1–2 MA/cm 2. Therefore, “self-epitaxy” is strongly expected to accelerate a practical conductor development due to its rapidly and highly texturing characteristic with the possibility to weaken the weak-link problem inherent in oxide superconductors.