Thin films of these spinels were grown by means of topotaxial solid-state reaction on (001) MgO substrates. The spinels differed widely in their lattice parameter, and this resulted in variations in the sign and degree of lattice misfit with respect to the substrate. The films were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopic selected-area electron diffraction and energy-dispersive X-ray micro-analysis. The spinel/MgO reaction fronts were investigated by using cross-sectional high-resolution electron microscopy. In the case of near-zero misfit (Mg2TiO4/MgO, Fe2MgO4/MgO), the films had an exact cube-to-cube orientation with respect to the substrate; with the spinel/MgO reaction front being completely coherent. During reaction, a network of cation antiphase boundaries formed in these films. In the case of non-vanishing misfit, semi-coherent reaction fronts occurred;with various interfacial defects forming, depending upon the sign and degree of the spinel/MgO lattice misfit. In the case of negative misfit (Al2MgO4/MgO, Cr2MgO4/MgO), the interfacial dislocations were edge dislocations; with their Burgers vectors lying in the interface plane. Together with the advancing reaction front, they moved via climb; emitting vacancies into the densely-packed lattices of spinel and MgO. In the case of positive misfit (In2MgO4/MgO), there existed a network of interfacial edge dislocations, with their Burgers vectors pointing out of the interface. The Burgers vector component that was perpendicular to the plane of the reaction front permitted these dislocations to glide in response to the advance of the reaction front. The system here avoided climb processes so as to prevent the emission of interstitial atoms into the densely-packed lattices. The latter process was expected to be unfavorable with regard to both the energetic and kinetic aspects. Due to the perpendicular Burgers vector component, the In2MgO4 films consisted of domains that were tilted by an angle of 3.5 away from the exact cube-to-cube orientation around 4 different <110> axes. The results were explained in terms of an interplay between the interfacial reaction mechanism and the properties of the interfacial dislocations which advanced with the reaction front.

H.Sieber, D.Hesse, P.Werner: Philosophical Magazine A, 1997, 75[4], 889-908