A GEOMETRICAL RATIONALIZATION OF THE SPECIAL PROPERTIES OF THE 14-DEGREES[001] GRAIN-BOUNDARY IN YBA2CU3O7-DELTA

14-degrees [001] tilt grain boundaries in YBa2Cu3O7-delta have been fo und to exhibit anomalously good superconducting critical currents, ass ociated with magnetic flux pinning, although no special interfacial st ructure has heretofore been associated with this misorientation. We pr esent an analysis of the geometry of the grain boundary in question an d show that it can correspond to a special interface, within the defin ition of constrained lattice coincidence, which may lead to new unders tanding of the superconducting behavior of grain boundaries. Our analy sis shows that the tetragonal-to-orthorhombic phase transformation may have important effects upon grain boundary structure and properties, indicating new approaches to producing high-current superconductors.