Interfacial control of reaction kinetics in oxides

The kinetics of nickel-aluminate spinel formation from the solid-state reaction of thin films of nickel oxide and two different orientations of single-crystal aluminum oxide has been measured. The spinel layer was found to thicken linearly with time, indicative of kinetic control by interfacial reaction. Furthermore, the linear kinetics were found to depend on the orientation of the aluminum oxide substrates, varying by nearly 2 orders of magnitude between the fastest and slowest. The monocrystalline substrate controls the crystallographic orientation of the overlayers (nickel oxide and spinel) and thereby the structure of the interfaces. The interfacial structure controls the kinetics of the interfacial or phase-boundary reactions. © 1996 The American Physical Society.