Evidence for weak link and anisotropy limitations on the transport critical current in bulk polycrystalline Y1Ba2Cu3Ox

Abstract

Measurements of the transport critical‐current density (J_c), magnetization J_c, and magnetoresistance in a number of bulk sintered samples of Y₁Ba₂Cu₃O_x from several different laboratories indicate that the transport J_c is limited by weak‐link regions between high J_c regions. The weak‐link J_c has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain‐boundary region in Y₁Ba₂Cu₃O_x shows no observable impurities or second phases to the scale of the [001] lattice planes (∼12 Å). The effect of intrinsic conduction anisotropy is discussed. A current‐transfer model is proposed in which weak conduction along the c axis plays a role in limiting J_c at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport J_c in bulk conductors.