A comparative study on in situ grown superconducting YBCO and YBCO-Ag thin films by PLD on polycrystalline SmBa_2NbO_6 substrate

摘要

The development and characterization ofStnBa_2NbO_6, which is a new ceramic substrate material for theYba_2Cu_3O_(7-#delta# )superconductor, are reported.SmBa_2NbO_6 has a complex cubic perovskite structure withlattice constant a = 8.524 A. The dielectric properties ofSmBa_2NbO_6 are in a range suitable for its use as a substrate formicrowave applications. SmBa_2NbO_6 was found to have athermal conductivity of 77 W m~-1 K~-1 and a thermal expansioncoefficient of 7.8 X 10~-6 beg C~-1 at room temperature.Superconducting Yba_2Cu_3O_7-s and Yba_2Cu_3O_(7-#delta#)-Ag thin films have been grown in situ on polycrystallineSmBa_2NbO_6 by the pulsed laser ablation technique. The filmsexhibited (001) orientation of an orthorhombic Yba_2Cu_3O_(7-#delta#) phase and gave a zero resistivity superconductingtransition (Tc(0)) at 90 K with a transition width of 1.5 K. Thecritical current density of YBCO-Ag thin films grown onpolycrystalline SmBa_2NbO_6 substrate was 3 X l0~5 A cm~-2 at77 K. A comparative study of YBCO and YBCO-Ag thin filmsdeveloped on polycrystalline SmBa_2NbO_6 substrate by PLDbased on the crystallinity, orientation and critical current density ofthe YBCO film is discussed in detail.