THE CHEMISTRY AND STRUCTURE OF (222)CDO AG HETEROPHASE INTERFACES ON AN ATOMIC-SCALE/

The chemistry and structure of {222} CdO/Ag (ceramic/metal) heterophas e interfaces are determined with sub-nanometer chemical and structural spatial resolution employing atom-probe field-ion and high-resolution electron microscopies. The interfaces are produced in a controlled ma nner via internal oxidation of a Ag-1.62at%Cd alloy, which results in the formation of CdO precipitates in a Ag matrix. The CdO precipitates are octahedral-shaped with facets on the {222} polar planes, and have a cube-on-cube orientation relationship with the Ag matrix. Atom-prob e analyses are made along the chemically-ordered CdO [111]-type direct ions, thereby perpendicularly intersecting the {222} interfaces. A tot al of 35 {222} heterophase interfaces is chemically analyzed, of which 19 have the chemical sequence Ag\O\Cd\... and 16 the sequence Ag\Cd\O \.... High resolution electron microscopy analyses reveal that the {22 2} facet planes of the CdO precipitates contain atomic height ledges, therefore indicating that the preciptates were in a coarsening stage. The combined atom-probe and high-resolution electron microscope result s demonstrate that the chemistry of the terminating {222} facet plane of CdO is controlled by coarsening kinetics.