Structure and electrical behaviour of grain boundaries allowing large critical currents in ceramic superconductors

Specific low energy boundaries in ceramic superconductors may be conducive to large critical currents. This was demonstrated on a MTG-textured YBa2Cu3O7-x. It was shown, with the electric microprobe method combined with the technique of microcontacts deposited by photolithography, that this material exhibits a dual electrical behaviour. High electrical barriers correspond to interfaces parallel to the texture direction which have a high energy, whereas cross-boundaries display a low electric barrier and a low energy. Our aim was to define the geometrical parameters of favourable boundaries, thus we studied polycrystalline ceramics with large grains which display a complete range of boundaries. The atomic structure of these boundaries was investigated by high resolution transmission electron microscopy and systematically correlated to their electrical barriers. (orig.)