Abstract
Geometrical modelling of grain boundaries is applied to determine the changes in their atomic structure as a result of atomic relaxation and reconstruction induced by deformation and diffusion processes. The energy associated with the primary and secondary coincidence tilt boundaries in the superconducting Y-Ba-Cu-O oxide is evaluated. The relaxed grain boundary configuration, wherein the surfaces coalesce to maintain continuity of the atomic planes, is obtained by minimization of the total energy of the boundary. The critical current density associated with the grain boundary is determined from the tunnelling behaviour of the superconducting pairs (electrons or holes) across internal boundaries. A quantitative model is presented to express the critical current density associated with the boundary as a function of the misorientation angle and these results are found to be in good agreement with available experimental data.