YBa₂Cu3O_7−x Thin Film Growth on Single Crystal and Polycrystalline Yttria-Stabilized Zirconia

Abstract

A variety of single crystal substrate materials have proven useful in obtaining high-quality epitaxial YBa₂Cu₃O_7−x (Y-123) thin films using several different growth techniques.^1–5 We have recently grown Y-123 thin films that routinely have T_c > 90 K and J_c > 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 J_c(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.