New buffer layer for high-temperature superconducting ceramics on sapphire: LaBa2Cu3Oy/Ag bilayers

Abstract

We have grown highly oriented LaBazCu,Oy (1 lO)/Ag (111) bilayers on sapphire (1120). This structure constitutes a potentially excellent buffer layer for the growth of l-2-3 ceramic oxides on sapphire substrates. This bilayer does not show superconductivity in resistive measurements. A DyBa2Cu30,, film grown on this bilayer also exhibited (110) orientation. Sapphire (a-A1203) is a desirable substrate for the growth of superconducting thin films due to its low dielectric constant and the extensive interest on silicon on sapphire technology. Unfortunately there exists a strong chemical interaction between sapphire and REBa,CusO,, (RE-123) ceramics'-3 which complicates the growth of high-quality-thin-film ceramic superconductors. Several reports on the growth of RE-123 superconducting thin films on sapphire substrate with and without buffer layerslm7 have shown that the quality of these films is inferior to that of films grown on other suitable substrates, e.g., SrTiO, and MgO. Witanachchi et a1.7 reported the growth of YBazC!u30,, (Y-123) films on sapphire (iO12) using Ag buffer layers, but no structural information was reported for the Ag nor the Y-123 films. Here we report the growth of LaBa2Cu30,, (La-123)/ Ag bilayers on sapphire (1120) substrates and show them to be excellent buffer layers for the growth of RE-123 films on sapphire. This structure has the inherent advantages that it is well matched to other RE-123 films and that it provides an excellent diffusion barrier. Moreover, to our knowledge, this is the first time that well oriented non-ctextured 123 films are grown on sapphire. This is significantly important for electronics applications because of the short superconducting coherence length along the c-axis of 2-3 A which makes non-c-textured 123 films preferable for Josephson and tunnel devices. All fabrication processes were performed in situ using magnetron sputtering. The RE-123 stoichiometric ceramic targets were prepared from better than 99.9% pure La203, DY+s, BaCO3,

Slow voltage oscillations in Ag-doped superconducting Y–Ba–Cu–O

“…The magnitude of voltage levels appearing in regular oscillations suggests that the physical case evolves in the intergranular region where the superconducting order parameter was suppressed by the addition of Ag and partly in the grains, since the grains have superconducting properties better than that of the weak link structure. As is well known, addition of Ag into the superconducting matrix improves the grain boundaries and also causes an increase in the normal state and superconducting properties of the corresponding material [10][11][12]. In a recent paper, we showed that the voltage oscillations in undoped YBCO take positive values with a background voltage value despite the fact that the driving current is bidirectional [4].…”

Domain growth of Dy2O3 buffer layers on SrTiO3

“…1) and LaiBa2Cu307 (Ref. 2) have been used as a buffer layer and a protection layer for single thin films as well as multilayers3 on MgO or SrTiO3. Other superconductor/buffer layer pairs exist such as (La, Sr)2CuO4/Sm2CuO4 (Ref.…”