Inclined Substrate Pulsed Laser Deposition of Ybco Thin Films on Polycrystalline Ag Substrates

Films of YBa2Cu3O7-x (YBCO) with c-axis orientation were directly deposited on nontextured silver substrates by inclined substrate pulsed laser ablation. The structure of the YBCO films was characterized by X-ray diffraction 2θ-scans, Ωscans, and pole-figure analysis. A good alignment of the c-axis of the YBCO films was confirmed by the Ω-scans, in which the full width at half maximum of the YBCO(005) was 3.8°. A sharp interface between the YBCO film and Ag substrate was observed by transmission electron microscopy. The surface morphology of the film, examined by scanning electron microscopy, reflected the recrystallization of the Ag substrate. Raman spectroscopy was used to evaluate the quality of the YBCO films. The superconducting transition temperature (Tc) and the critical current density (Jc) of the films were determined by inductive and transport measurements, respectively. Tc = 91 K with a sharp transition and Jc = 2.7 × 10A/cm at 77 K in zero external field were achieved on a film with 0.14μm thickness. INTRODUCTION A promising material for future electric power applications is YBa2Cu3O7-x (YBCO)-coated conductors [1-4]. Recently, YBCO thin films grown on silver tapes have attracted much interest because of their high superconducting transition temperature (Tc) and high critical current density (Jc). Silver is an ideal substrate candidate due to its compatibility with YBCO and its inertness to oxidation [5-6]. The electrical properties have been improved in the YBCO films by silver doping up to 20 at.% [7-8]. Unlike other substrate materials such as Nibased alloys, in which buffer layers are necessary to prevent Ni diffusion into the YBCO film, YBCO can be directly deposited on silver substrate without a buffer layer. To achieve high Jc, textured silver sheets are often chosen as substrates. YBCO films grown on these textured substrates have achieved Jc of ≈ 5×10 A/cm [9-11]. However, a relatively complex process is usually involved in preparing well-textured silver substrate for YBCO deposition. We have explored direct deposition of YBCO on nontextured silver substrate for simplifying the fabrication process. In our studies, nontextured polycrystalline silver sheet was used as the substrate, and YBCO films were directly deposited on these substrates by inclined substrate pulsed laser deposition (IS-PLD). Inclined substrate deposition is a promising technique for growing biaxially textured films on nontextured substrates [3-4], and improvement in film quality is expected from this technique. This work shows the feasibility for fabricating high-Jc YBCO films on nontextured polycrystalline silver substrate. EXPERIMENTAL Inclined substrate PLD was used to grow YBCO films. A schematic diagram of the deposition system is shown in Figure 1. Substrates with silver paste were mounted on a tiltable heater. Different from the conventional arrangement in which the surfaces of the target and the heater were parallel, the heater can be tilted at an angle with respect to the target surface. The substrate inclination angle, α, substrate normal with respect to the evaporation plume direction, was typically set at 55°, which is believed to be a favorable angle to produce (001) oriented textured film. To compare the dependence of α, 35° and 72° were also tested. Nontextured polycrystalline silver coupons, 5×10 mm in dimensions and 0.1 mm in thickness, were used as substrates after mechanical polishing with α Pulsed Excimer Laser Ag Substrate Tilted Heater Rotating Target Plasma Plume