High-resolution electron microscopy of ZnO grain boundaries in bicrystals obtained by the solid-phase intergrowth process

Bicrystals of ZnO with large interfacial areas and controlled misorientations have been prepared by the solid-phase intergrowth method. The structure of three [0001] tilt boundaries with misorientations of less than 1 degrees, 17.8+/-0.1 degrees and 31.5+/-0.1 degrees have been studied by high-resolution electron microscopy. The low-angle boundary comprised well separated crystal dislocations and the atomic structure of the large-angle boundaries could be described in terms of sequences of [0001] tunnels coordinated fivefold, sixfold and sevenfold by atomic columns. The 17.8 degrees asymmetric ((8) over bar 17 (9) over bar 0) boundary (Sigma=31) was planar, exhibiting a relatively long-period repeating structure and was occasionally interrupted by interfacial dislocations. The Burgers vector and step character of these defects were investigated using circuit mapping and found to be consistent with topological theory. The 31.5 degrees interface was found to be extensively facetted into ((2) over bar 7 (5) over bar 0) and (13 (4) over bar 0) symmetric tilt boundaries. Mirror symmetry in the immediate deviation of -0.7 degrees from the periodic Sigma=13 system was observed to be accommodated by primitive interfacial dislocations. Some of these defects exhibited compact cores, introducing minimal disruption to the underlying others showed a more complex reconstruction, leading to a reduction in interfacial area and defect energy.