Atomic resolution electron microscopy studies of reaction fronts in spinel-forming solid state reactions

The structure of reaction fronts in different systems were investigated using HRTEM. The Al2O3 (<1(1)over bar .2>) MgAl2O4 (001) reaction front shows different structures along its interface, from an incoherent one (untilted) to a semi-coherent one with a systematic tilt (2 to 5.8 degrees) of the spinel lattice. However, MgO(001)/MgIn2O4 (001) reaction fronts consist of coherent regions separated by misfit dislocations. The MgIn2O4 initially grows in a tilted orientation (similar to+/-3.5 degrees) around two different [110] axes. At a later stage (when the MgIn(2)O4 thickness is well above 1 mu m), the Mgln(2)O(4) grows in a perfect [001] orientation. The reason for this is discussed in terms of the reaction initially being interface-controlled and later being diffusion-controlled.