Four Nb/Al2O3 interfaces were generated by depositing Nb onto (00•1), (01•0), (¯21•0) and (01•2) -phase (sapphire) surfaces by means of molecular beam epitaxy. High-resolution transmission electron microscopy showed that the interfaces were semi-coherent at the thicknesses which were investigated. Coherent regions alternated with misfit dislocations at the interfaces. The visible displacement field around the cores of the dislocations was restricted to the Nb lattice, and the Burgers vector of the misfit dislocations was therefore attributed to the Nb lattice. The Burgers vector was determined, using high-resolution transmission electron microscopy, by invoking the concept of a Burgers circuit around the core of the misfit dislocations. This core was usually at the interface, and the Burgers circuit therefore had to cross the interface. The dislocation networks which accommodated the mismatch between the Nb lattice and the sapphire were built up of misfit dislocations with a Burgers vector of ½<111>. This vector corresponded to the Burgers vector of bulk dislocations in Nb. The Burgers vector of the misfit dislocations was not always parallel to the interface, and not all of the misfit dislocations were pure edge dislocations. Only the edge component of the Burgers vector which was parallel to the interface accommodated the lattice mismatch at the interfaces. Screw and/or edge components which were perpendicular to the interface were usually compensated in the networks. Only in the system where the interface was parallel to (01•2) did an array of misfit dislocations with an uncompensated Burgers vector component lead to a tilt of the Nb lattice with respect to the sapphire lattice.

G.Gutekunst, J.Mayer, V.Vitek, M.Rühle: Philosophical Magazine A, 1997, 75[5], 1357-82