Structure of misfit dislocations in niobium-sapphire interfaces and strength of interfacial bonding: An atomistic study

The formation of networks of misfit dislocations is investigated at the (00 01)(Al2O3)\\(111)(Nb) interface using a recently proposed approach (Vitek e t al., Phil. Mag. A, 1995, 71, 1219) which employs a very simple pair-poten tial to describe interaction between the metal and the substrate that conta ins the strength of interfacial adhesion as a parameter. The calculations d emonstrate how the strength of bonding between the two materials decides bo th the form of the network and the atomic structure of the cores of these d islocations. At the same time it reveals that diffusion is essential for th e formation of the observed triangular network of 1/2[111] dislocations. Th e calculated structures are then used to investigate related high resolutio n electron microscope (HREM) images using a multislice technique. In these simulations translational symmetry along the electron beam was not assumed but for each slice of material along the beam different sub-structures were used. This allowed us to investigate fully the effect of the dislocation i ntersections upon the images of the dislocation cores. Their effect is, ind eed, considerable if an intersection is in the region producing the image b ut if not, the images of the cores of misfit dislocations are affected only marginally and HREM can capture fine details of the core structure. A dire ct comparison of an experimental observation in Mayer and co-workers (Acta metall. mater., 1992, 40, S217; Scripta metall. mater., 1994, 31, 1097) wit h the present simulations demonstrates this ability. (C) 1999 Acta Metallur gica Inc. Published by Elsevier Science Ltd. All rights reserved.