Capacitance as a probe of high angle grain boundary transport in oxide superconductors

We report a series of studies of grain boundary (GB) capacitance for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films grown on SrTiO/sub 3/ (STO) bicrystal substrates. By varying the film thickness and the width of the track containing the GB, we find that the substrate makes no contribution to the capacitance measured using Fiske resonances or hysteresis in most cases. This is due to the frequency dependence of the dielectric properties of SrTiO/sub 3/. We have also found that GB capacitance per unit area c/sub GB/ correlates with the resistance-area product R/sub n/A. For our own GBs and GBs reported in the literature the data is is consistent with c/sub GB//spl prop/(R/sub n/A)/sup -1/. We attribute this to variations in GB barrier properties, which reduce the active area, whilst maintaining locally the transport mechanism as tunneling.