A comparative study on in situ grown superconducting YBCO and YBCO-Ag thin films by PLD on polycrystalline SmBa2NbO6 substrate

The development and characterization of SmBa2NbO6, which is a new ceramic substrate material for the YBa2Cu3O7-δ superconductor, are reported. SmBa2NbO6 has a complex cubic perovskite structure with lattice constant a = 8.524 A. The dielectric properties of SmBa2NbO6 are in a range suitable for its use as a substrate for microwave applications. SmBa2NbO6 was found to have a thermal conductivity of 77 W m-1 K-1 and a thermal expansion coefficient of 7.8x10-6 deg. C-1 at room temperature. Superconducting YBa2 Cu3O7-δ and YBa2Cu3O7-δ -Ag thin films have been grown in situ on polycrystalline SmBa2NbO6 by the pulsed laser ablation technique. The films exhibited (00l) orientation of an orthorhombic YBa2 Cu3O7-δ phase and gave a zero resistivity superconducting transition (TC(0)) at 90 K with a transition width of ∼1.5 K. The critical current density of YBCO-Ag thin films grown on polycrystalline SmBa2NbO6 substrate was ∼3x105 A cm-2 at 77 K. A comparative study of YBCO and YBCO-Ag thin films developed on polycrystalline SmBa2NbO6 substrate by PLD based on the crystallinity, orientation and critical current density of the YBCO film is discussed in detail. (author)