Abstract
Through novel use of beam irradiation during scanning transmission electron microscopy (STEM) observations, the relative binding energies for rare earth atoms (Gd) at different adsorption sites on the prismatic grain surfaces in Si3N4 ceramics have been successfully measured. Site-specific binding strengths of interfacial adsorbates in bulk ceramics containing amorphous intergranular films and amorphous pockets at multigrain junctions have, until now eluded researchers. With the approach described here, theoretically predicted differences in the adsorption energies of rare earths at internal interfaces can be directly assessed. This technique has also identified the decrease in stability of successive planes of ordered rare earth atoms paralleling the grain surfaces as a function of position out into the amorphous pockets. The findings bring forward a critical test of the theoretical concepts that now provide the understanding of segregation and adsorption behavior in a complex, multi-component ceramic. Such wetting behavior (by rare earth additions) dictates phase transformation and, therefore, microstructural evolution processes. The observations made in this study provide confirmation of calculated relative strengths of bonding at different interfacial sites and can therefore be used for both tailoring new functional ceramic microstructures, with atomic level descriptions of their macroscopic mechanical properties