Microscopic origins of the grain boundary effect on the critical current in superconducting copper oxides

General relations between the local atomic structure and properties of grain boundaries (GBs) in superconducting copper oxides are described. The results are based on the complex experimental and theoretical study, which includes: (1) the transmission electron microscopy characterization of GBs in the bulk materials, (2) GB atomic structure simulation, (3) first-principles calculations and modelling of the electron structure modification, crystal lattice relaxation and intergrain bond formation near the GBs simulated. The number of broken Cu-O bonds, the degree of electron state perturbation at the GB and the role of crystal lattice relaxation are found to be strongly dependent on the GB topology.