Dell J. St. Julien

Y‐Ba‐Cu‐O thin films grown on rigid and flexible polycrystalline yttria‐stabilized zirconia by pulsed laser ablation

In situ growth of highly oriented YBa2Cu3O7−x thin films (200–500 nm in thickness) has been obtained by pulsed KrF (248 nm) laser ablation on both rigid and flexible randomly oriented polycrystalline yttria‐stabilized zirconia substrates. It is shown that c‐axis‐perpendicular YBa2Cu3O7−x films with a mosaic spread of only 1.0° can be grown on these randomly oriented polycrystalline substrates. Superconducting thin films were obtained with Tc(R=0)∼89 K on well‐polished substrates. For the films deposited on the flexible substrates, the superconducting Tc is not degraded by repeated bending of the flexible substrate/film composite over a 2.25‐cm‐radius arc although the normal‐state resistivity increases slightly, suggesting the creation of microcracks. The YBa2Cu3O7−x films grown on rigid polycrystalline yttria‐stabilized zirconia substrates have a critical current density Jc(H=0)∼1400 A/cm2 at 77 K.

BSCCO-2212 thick films on a flexible YSZ substrate

Abstract The potential use of flexible YSZ as a substrate material for the partial-melt growth, PMG, of Bi-2212 thick films was studied. Results show low critical temperatures, T c , ( T c was significantly improved (> 80 K) when Ag was used as a buffer layer. The optimum peak processing temperatures were found to decrease with increasing buffer-layer thickness. The critical current density, J c , also improved with increasing buffer-layer thickness. The self-field J c of these Bi-2212/Ag/YSZ composites was 1−3×10 3 A / cm 2 at 20 K, significantly lower than that for the Bi-2212/Ag tapes. However, the present study strongly supports the viability of using flexible YSZ with an appropriate buffer in the wind-and-react fabrication of high- T c pancake coils. The microstructure and transport properties of Bi-2212/YSZ and Bi-2212/Ag/YSZ composite structures will be discussed.

YBa2Cu3O7−x Thin Film Growth on Single Crystal and Polycrystalline Yttria-Stabilized Zirconia

A variety of single crystal substrate materials have proven useful in obtaining high-quality epitaxial YBa2Cu3O7−x (Y-123) thin films using several different growth techniques.1–5 We have recently grown Y-123 thin films that routinely have Tc > 90 K and Jc > 1 M A/c m2 by pulsed-laser ablation of a stoichiometric, polycrystalline Y-123 target on single crystal substrates such as (100) SrTiO3, LaA1O3, KTaO3 and yttria-stabilized zirconia (YSZ).2 For many applications, however, single crystal substrates are not appropriate due in part to the substrate cost and/or the lack of substrates of appropriate dimensions and flexibility. For this reason, a great deal of effort has been put into developing high-temperature superconducting conductors which would be more suitable for applications. These efforts have included Ag-sheathed Y-123, Tl-Ba-Ca-Cu-O and Bi-Sr-Ca-Cu-O superconducting wires and tapes,6–8 magnetically- and melt-textured bulk materials,9,10 as well as Y-123 thin films on polycrystalline metallic substrates.11 However, recent work has shown that the presence of large-angle grain boundaries in Y-123 causes a reduction in Jc(H=0) by a factor of ~1/50.12 It appears that a high degree of crystalline alignment is necessary to obtain critical current densities approaching those necessary for most high-temperature superconducting applications to be realized. This is partly a consequence of the anisotropy in these materials which requires that conduction in the superconducting state occurs primarily within the a-b planes.