Direct observation of the reduction of moo 3 at low temperatures

Abstract

An electron microscope study has been carried out of the reduction of MoO 3 by hydrogen and carbon monoxide in a gas reaction cell in an AEI EM7 1 MeV electron microscope. At temperatures below 80 °C, line defects deviating a few degrees from [101] are generated at a depth of about 200 Å below the crystal surface; the presence of platinum was found to be essential for the effects to be observed. The line defects are found to be partial screw dislocations bounding stacking faults extending from the surface. The nature of these dislocations is such that they tend to accommodate the misfit between the reduced surface layer and the underlying matrix. The reduction is thought to be accompanied by the generation of anion vacancies which diffuse slowly into the crystal; by identifying the depth of the dislocation with the diffusion front (and in other ways), the activation energy for migration of anion vacancies is estimated to be about 0.85–0.9 eV.