EXPLANATION OF LOW CRITICAL CURRENTS IN FLAT, BULK VERSUS MEANDERING,THIN-FILM [001]-ILT BICRYSTAL GRAIN-BOUNDARIES IN YBA2CU3O7

Thin-film and bulk [001] tilt, bicrystal grain boundaries in YBa2Cu3O7 exhibit a strong dependence of critical current density on misorienta tion angle. What is particularly difficult to understand is its thirty times lower magnitude in bulk grain boundaries which are microscopica lly more perfect, i.e., flatter, minimally faceted, and free of impuri ty phases. A plausible explanation, based on differences of the pinnin g of Josephson vortices in these grain boundary types, is proposed her e. [S0163-1829(98)05438-1].