Granularity controlled percolative current conduction in YBa₂Cu₃O₇/Ag composite thick films

Abstract

Temperature-dependent electrical resistivity in a set of YBa 2 Cu 3 O 7 /Ag thick films prepared by reaction diffusion technique is analysed to estimate the extent of granularity in them. Percolative nature of charge transfer in the films was examined by studying the excess conductivity in the superconducting order parameter fluctuation (SCOPF) region (T T c ), the approach to zero-resistance state in the tail region, the current-controlled tailing of the resistivity transition near T c 0 (T c 0 < T < T c 0 ) and the current-voltage characteristics in the paracoherent regime (T < T c 0 ) with their associated exponents. The percolative current model was thus utilized to quantify granularity in the films of such parameters like the weak link resistivity across grain boundaries, current path lengthening factor arising due to grain misalignment, and due to voids and cracks. Evolution of these parameters with Ag content in the films indicates reduced structural defects (voids and cracks) at higher Ag concentrations. The result points to a mechanism of grain growth in the composites, which accounts for the improved grain growth with narrower grain size distribution in these systems as compared to that in Ag-free YBCO sintered material. These microstructural modifications cause lowering of percolation threshold from the value expected in a granular system where the grain size approaches to one of the system dimensions (the film thickness) making the conduction through grain boundary essentially two-dimensional.

Intergranular percolation in granular YBCO/BaTiO3 composites

“…any signature of phase transition. This problem is analogous to our previous study in YBCO/Ag composite, where Ag diffuses into the grains [6].…”

Fluctuation conductivity and inhomogeneity in granular YBa2Cu3O7−y/Ag composite thick films

“…The approach to this state from T c in the form of tailing (figure 1) indicates that Josephson tunnelling across the grain boundary weak links progressively couples the superconducting grains to each other. This type of tailing feature in the resistive transition close to T c0 has been seen mostly in granular superconductors [24], where mesoscopic inhomogeneities like secondary phases, grain boundaries, twin boundaries, cracks and voids influence the occurrence of global superconductivity in the sample. The YBCO/Ag composite thick films represent a class of granular superconductor where the charge transport occurs in an interpenetrating superconducting and normal state percolative medium.…”

“…The YBCO/Ag composite thick films represent a class of granular superconductor where the charge transport occurs in an interpenetrating superconducting and normal state percolative medium. In YBCO/Ag composites, it is believed that Ag resides at the grain boundaries and modifies the microstructure of the sample to a large extent [24]. The observed decrease of T c0 (figure 4) is therefore a consequence of the progressive decoupling of the superconducting grains with increasing Ag content in the films.…”

Selective disorder in the CuO basal planes of YBa2Cu3O7−y by swift heavy ion induced secondary electrons

“…1) has been seen mostly in granular superconductors where mesoscopic inhomogeneities like grain boundaries, twin boundaries, cracks and voids influence the occurrence of global superconductivity in the sample [11,12]. The T c0 characterizes the onset of global superconductivity in the sample, where long range superconduc- ting order is achieved.…”