Probing the initial stages of solid-state reactions by total reflection EXAFS (reflEXAFS)

The effectiveness of reflEXAFS as a probe for the very initial stages of solid-state reactions has been investigated by studying the local chemical environment of Ni during the reaction of a 150 Angstrom thick film of NiO deposited onto Al2O3. The reaction to give the spinel phase requires temperatures about 1000 degreesC, and reaction progress degrees could be obtained by increasing the firing time at high temperature. At lower temperatures (congruent to930 degreesC), a structural rearrangement in the NiO film could be detected, seemingly related to the process by which local chemical equilibrium is attained at the interface. This should be regarded as the very early stage of the solid-state reaction and therefore this experiment proves the feasibility of a reflEXAFS investigation on these aspects of solid-state chemistry. (C) 2002 Elsevier Science B.V. All rights reserved.