The capacitance of 24°͓001͔ tilt calcium doped Y 1−x Ca x Ba 2 Cu 3 O 7−␦ grain boundaries has been measured for thin films with x in the range 0.0-0.3. The capacitance was determined from the hysteresis in the I-V characteristic. By measuring the capacitance as a function of the voltage across the junctions it was possible to observe the contribution of both parasitic substrate capacitance and heating to the hysteresis. These effects enable the determination of the intrinsic capacitance of the grain boundaries. The effect of thermal noise on the measurement is also assessed, and found to be much less than the observed changes in the capacitance. The capacitance is found to increase as the calcium doping increases: from 0.2 Fm −2 for x = 0.0 to a maximum of 1.2 Fm −2 for x = 0.3. The changes in the capacitance per unit area are observed to be inversely proportional to the corresponding changes in the resistance area product.

Abstruct-We report a series of studies of grain boundary (GB) capacitance for YBazCu30,-s (YBCO) films grown on SrTi03 (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 SrTi03. We have also found that GB capacitance per unit area cGB correlates with the resistance-area product R,A. For our own GBs and GBs reported in the literature the data is is consistent with c G p ( R J ) -' . We attribute this to variations in GB barrier properties, which reduce the active area, whilst maintaining locally the transport mechanism as tunneling.

No abstract

No abstract

No abstract