Transport-critical-current behaviour and grain boundary microstructure in YBa2Cu3Ox

Abstract
The microstructures of polycrystalline YBa2Cu3Ox samples were varied through different sintering mechanisms to study transport-current characteristics in magnetic fields. TEM experimental results indicate that the transport critical current in polycrystalline YBa2Cu3Ox is closely correlated with grain boundary microstructures. Specifically, the Jc(H) is severely suppressed as the grain boundaries are contaminated with the second phases. The field required for the Jc(H) values to decrease to zero is also strongly affected by the grain boundary microstructure. The critical-current behaviour and closely related microstructural changes are explained with Josephson weak-link and flux-flow models.