SUPERCONDUCTING YBA2CU3O7-DELTA-AG THIN-FILMS (T-C(0)=90K) BY PULSED-LASER DEPOSITION ON POLYCRYSTALLINE BA2NDNBO6 - A NOVEL SUBSTRATE FOR YBA2CU3O7-DELTA FILMS

The development and characterisation of Ba2NdNbO6, a novel ceramic sub strate material for YBa2Cu3O7-delta superconductor, are reported. Ba2N dNbO6 has a complex cubic perovskite structure [A(2)(BB')O-6] with lat tice constant a = 8.573 Angstrom. The dielectric properties of Ba2NdNb O6 are in a range suitable for its use as a substrate for microwave ap plications. Ba2NdNbO6 was found to have a thermal expansion coefficien t of 8.6 x 10(-6) degrees C-1 and a thermal conductivity of 87 W.m(-1) .K-1. Superconducting YBa2Cu3O7-delta-Ag thin films have been grown in situ on polycrystalline Ba2NdNbO6 by pulsed laser ablation technique and the optimum conditions have been established. The films exhibited (00l) orientation of an orthorhombic YBa2Cu3O7-delta phase and gave a zero resistivity superconducting transition [T-C(0)] at 90 K with a tr ansition width of similar to 1.5 K and J(C) similar to 3 x 10(5) A/cm( 2) at 77 K.