Spinel films with thicknesses of up to 4 were grown by means of topotaxial solid-state reaction on MgO (001) substrates. 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 atomic structure of the spinel/MgO reaction front was investigated by means of cross-sectional high-resolution transmission electron microscopy. A network of misfit dislocations was shown to accommodate a lattice mismatch of +4.5% along the MgO/In2MgO4 interface. This network had to move together with the advancing reaction front. In the case of thin films, with reaction occurring in the interface-controlled regime, the Burgers vectors of the network dislocations pointed out of the interface plane. This permitted the misfit dislocations to glide easily during reaction. In the case of thick films, with the reaction probably occurring in the diffusion-controlled regime, the Burgers vectors lay in the interface plane. In this regime, the dislocations had to climb during reaction. Slow and energetically unfavorable climb processes did not limit the reaction rate, since it was now controlled by the slower diffusion process. A model dislocation reaction was used in order to explain the transition from one reaction regime to the other.

H.Sieber, P.Werner, D.Hesse: Philosophical Magazine A, 1997, 75[4], 909-24