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 misorien tations 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 s tudied 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 sequence s of [0001] tunnels coordinated fivefold, sixfold and sevenfold by ato mic columns. The 17.8 degrees asymmetric ((8) over bar 17 (9) over bar 0) boundary (Sigma=31) was planar, exhibiting a relatively long-perio d repeating structure and was occasionally interrupted by interfacial dislocations. The Burgers vector and step character of these defects w ere investigated using circuit mapping and found to be consistent with topological theory. The 31.5 degrees interface was found to be extens ively facetted into ((2) over bar 7 (5) over bar 0) and (13 (4) over b ar 0) symmetric tilt boundaries. Mirror symmetry in the immediate devi ation of -0.7 degrees from the periodic Sigma=13 system was observed t o be accommodated by primitive interfacial dislocations. Some of these defects exhibited compact cores, introducing minimal disruption to th e underlying others showed a more complex reconstruction, leading to a reduction in interfacial area and defect energy.