Fabrication and superconducting transport properties of bicrystal grain boundary Josephson junctions on different substrates

We have reproducibly fabricated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) grain boundary Josephson junctions (GBJs) on SrTiO/sub 3/ and MgO bicrystals as well as by introducing buffer layers between the c-axis oriented YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// film and the SrTiO/sub 3/ bicrystal substrate. For the additional layers non-superconducting Nd/sub 1.85/Ce/sub 0.15/CuO/sub x/ (NCCO) and NdGaO/sub 3/ were used. The effect of the layer structure on the superconducting transport properties of the GBJs was analyzed by measuring the current-voltage characteristics (IVCs), their derivatives, the resistive transition R(T), and the magnetic field dependence of the critical current I/sub c/(B). YBCO-GBJs fabricated on MgO and SrTiO/sub 3/ bicrystal substrates were found to have very similar low frequency characteristics. Fiske resonances were investigated to obtain information on the high-frequency properties. The Swihart velocity was found to be considerably smaller for GBJs fabricated on SrTiO/sub 3/ as compared to MgO due to the large relative dielectric constant of SrTiO/sub 3/ and the related stray capacitance.<
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