Mechanisms of Reactions in the Solid State: (110) Al2O3 + (001) ZnO Interfacial Reaction

The mechanisms of the (110) Al2O3 + (001) ZnO interfacial reaction, that eventually yields the spinel ZnAl2O4, has been studied using a multitechnique approach involving local- and long-range structural probes (EXAFS, μ-XANES, and XRPD) and a surface analytical probe such as SIMS. It is demonstrated that the reaction involves a series of different steps, where at least two different nonequilibrium compounds are formed and then transformed into the spinel. One of these compounds, playing a role similar to reactive intermediates in solution chemistry, has been trapped. To the best of our knowledge, this is the first time that such a kind of behavior has been demonstrated for a heterogeneous solid state reaction. It is argued that the critical step is a concerted, homogeneous movement of a set of atoms, rather than long-range diffusion. The implications of these findings for the fabrication of ceramic and nanoscale materials are discussed.