Critical current in high-temperature superconductors with disordered tilt grain boundaries

Abstract

A model is suggested to describe the effect of tilt grain boundaries with partly random dislocation distribution on the critical current value in high-temperature superconductors. Within this model, the field of grain-boundary stresses σ_αβ acquires a much more pronounced long-range character than in the case of a periodic dislocation arrangement. At large distances x from a tilt grain boundary, σ_αβ ∝ x ^−3/2 (which corresponds to the quasi-equidistant dislocation walls), whereas at small x, we have σ_αβ ∝ x ^−1/2 (which corresponds to randomly arranged dislocation walls). A region with stresses exceeding a certain critical value is treated as the region of normal metal, and, therefore, the critical current passing through this region decreases exponentially. It is shown that the model suggested satisfactorily agrees with experimental data.