Professor Tom Vogt, NanoCenter & Department of Chemistry, University of South Carolina
High-Angle-Annular-Dark-Field/Scanning Transmission Electron Microscopy (HAADF/STEM) is a technique uniquely suited for detailed studies of the structure and composition of complex oxides. The HAADF detector collects electrons which have interact inelastically with the potentials of the atoms in the specimen and therefore resembles the better known Z2 (Z is atomic number) Rutherford scattering. One class of important catalysts consists of bronzes based on pentagonal {Mo6O21} building units; these include Mo5O14 and Mo17O47. In the last 20 years, new materials doped with a variety of substitution elements, but built upon the same structural building units, have been made and evaluated for their catalytic properties. Applications include the selective oxidation of light paraffins and olefins, as well as the partial oxidation of methanol.
We present HAADF-STEM investigations of various complex oxide phases and show that we can for example distinguish metal-containing sites within these structurally and compositionally complex-oxides through the analysis of contrast. We compare our experiments to image simulations. We also utilize the enhanced spatial resolution provided by aberration-corrected HAADF STEM imaging to characterize the nature of registry between structurally distinct intergrown phases in the Mo-V-O system. Based on the atomically resolved images, structural models describing the nature of these phase boundaries are developed.
