The 45° grain boundaries in YBa₂Cu₃O_7−δ

High-angle grain boundaries in YBa₂Cu₃O_7−δthin films are of technological interest because of the weak coupling observed between the grains; however, not all high-angle grain boundaries show this weak-link behavior. The microstructure of both these boundaries is not understood, nor is the reason for the differing electrical transport properties. High-angle grain boundaries in YBa₂Cu₃O_7−δthin films on MgO, where the angular misorientation between the grains is ∼45°, have been examined using high-resolution electron microscopy. The results show that the boundary structure can appear quite different even when the angular misorientation between the two grains is the same. The stability of the grain boundaries under the electron irradiation in the electron microscope was found to be a function of the accelerating voltage—400 kV leads to rapid disordering of the boundary region.