Kinetics of Thin‐Film Reactions of Nickel Oxide with Alumina: II, {1100} and {1102} Reaction Couples

The kinetics of the earliest stages of solid‐state reactions between epitactic thin films of nickel oxide (NiO) and {11# 00}‐ and {11# 02}‐oriented single crystals of alumina (Al 2 O 3 ) have been studied. The starting reaction geometry consisted of a nickel aluminate (NiAl 2 O 4 ) buffer layer 20 nm thick and a NiO overlayer that was 400 nm thick, both of which were grown via pulsed‐laser deposition and were epitactic with the substrate. When heated, the reaction lay‐ers thickened mainly as the square root of time (i.e., para‐bolic kinetics) increased, which was indicative of reaction‐controlled kinetics via diffusion through the product layer. The activation energy for the reaction was 461 kJ/mol for {11# 00} and 464 kJ/mol for the {11# 02}; both values are consistent with measurements made previously using thin‐film and bulk reaction geometries. A smaller linear component to the kinetics has also been identified. The results of microstructural characterization and “marker” experiments will also be discussed.