PERCOLATION AND ELECTRICAL-RESISTIVITY IN THE YBA2CU3O7-AG COMPOSITE SYSTEM

We have measured the resistivity of the YBa2Cu3O7-Ag composite system with Ag volume fraction, pAg ranging from 0-100%. The percolation behavior and the normal-state resistivity are studied. We find a three-dimensional threshold for the Ag matrix occurring at pAg ≅20% and a threshold for the superconducting matrix occurring at 1-pAg≅30%. The electrical resistivity is interpreted in terms of a resistivity model for granular YBa2Cu3O7 proposed by Halbritter et al. [Z. Phys. B -Condensed Matter 71, 411 (1988)]. Based on this model, we show that the resistivities between the YBa2Cu3O7 grains and flaws in the grains are greatly diminished in the samples, indicating significantly improved grain growth behavior of the YBa2Cu3O7 phase resulting from the addition of Ag. With the diminishing of the grain boundary resistivities, an "intrinsic" value for the temperature coefficient of resistivity, (1/gr)(dρ/d T), can be inferred, which is 3.3×10-3/K at 300 K. This value is very close to that observed in the Cu-O2 planes in single crystals and epitaxial films of YBa2Cu3O7. © 1990 Springer-Verlag.