Crystallography of Boundaries and Interfaces

Abstract

Internal interfaces in solids influence and/or even control essential properties of materials. In order to have a thorough understanding of structure-property correlations, systematical investigations of the atomic stucture of interfaces and boundaries are necessary. The atomic stucture of interfaces and boundaries can be determined by high-resolution electron microscopy (HREM). The different techniques of analytical electron microscopy (energy-dispersive X-ray spectroscopy — EDX, electron energy loss spectroscopy — EELS, and convergent beam electron diffraction — CBED) provide the required information on the chemical composition of the interface regions. In order to determine the equilibrium stucture and the energy of an interface, atomistic simulations of the interface stucture have to be carried out. The relaxed interface stucture may be simulated applying molecular dynamical (MD) calculations and the methods of static energy minimization (MS). For all interface calculations a suitable geometrical model has to be generated (construction of the computational cell). Then, the interatomic interaction process as well as the relaxation process have to be taken into consideration. In the following various crystallographic concepts of characterizing interface stuctures are treated. In general, the determination of the symmetry of the two adjacent crystals and of that of the interfaces between them is very important both for the analysis and the prediction of possible interface structures. A useful classification scheme for crystalline interfaces is to distinguish between homophaseand heterophase boundaries, sometimes also denoted as grain boundaries and interphase boundaries, respectively. Homophase boundaries are interfaces between two crystals with the same crystal structure and the same chemical composition. Grain boundaries and other