Atomic structure of metallic interfaces

The atomic structure of the (310) symmetric tilt grain boundary in Nb and of an interface between Mo and Re is calculated. The calculations are done within the tight binding (TB) approximation to quantum mechanics and are checked carefully against some accurate first-principles calculations in the local density approximation to density functional theory. A non-orthogonal spd electron TB model is tested, but is found to be no improvement on the much simpler orthogonal d-electron model; in particular there is no improvement in the volume dependence of the total energy. The structure of the Nb grain boundary is compared to that obtained by other authors using high resolution electron microscopy. The comparison enables some statements to be made about the nature of the interatomic interactions and especially about the opposing forces that are balanced at the equilibrium grain boundary expansion. The paper includes the first quantum mechanical calculation of a dissimilar metal interface with a view to obtaining the structure of a misfit dislocation and a value for the theoretical strength of the interface. It is concluded that the misfit dislocation in this case has a widely spread core and that the theoretical strength is considerably reduced relative to the bulk crystal