Theoretical Investigation of Interfaces

The proper treatment of defects is one of the major tasks in materials design, because defects are responsible for the either desirable or detrimental deviations between the characteristics of the material to be tuned and the well-known properties of an ideal crystal. Microelectronic devices work because of clever point defect engineering, line defects govern plastic deformation processes, and interfaces determine the mechanical stability of composite materials. Especially interfaces gain importance with the current trend towards nanoscale materials; first, the surface-to-volume ratio is strongly increased in nanocrystalline material, and, second, stable arrangements of point or line defects require a minimum crystallite size, which can be larger than the actual nanocrystallites. Thus, the present chapter gives an introduction into the most common approaches for modeling interface properties. We introduce the basic concepts of interface symmetry, structure and analysis with a strong focus on the theoretical methods and give an overview of currently available techniques for the modeling and simulation of the interface properties at an atomic-scale level. Two fundamentally different interface types are distinguished: The discussion of the homophase boundary properties is focussed on oxide grain boundaries, which we studied extensively in comparison with amply available experimental observations. For the heterophase boundaries examples of non-reactive, reactively doped, and inherently reactive boundaries are presented. A special focus lies on the interfaces between metals and oxides where the discrepancy of the material properties across the interface is most prominent and all three bonding situations can occur: weak adhesion between inert fragments, activated adhesion upon doping, and strong adhesion.