Interfacial atomic structure and supercurrent attenuation by grain boundaries in YBa2Cu3O7-x ceramics

Two types of boundaries can be observed in polycrystalline ceramics. The most frequent type hold the (ab) plane. The most striking example is given by the coincidence ΣQ3 boundary (c1 perpendicular to c2) which exhibits a highly continuous atomic structure. The second type do not hold the (ab) plane. It is shown that its interfacial atomic structure is disturbed on a few atomic planes only. Furthermore this structure becomes nearly perfect when abutting grains present a coincidence relationship. In parallel, local critical current measurements have been carried out on these different types of boundaries. It is shown that only coincidence boundaries which do not hold the (ab) plane display a weak attenuation of the supercurrent. (orig.)