It is shown that the rare earths (REs) have different tendencies to
segregate to the grain surfaces in silicon nitride ceramics, and this
alters the filling of adsorption sites on the prismatic plane surfaces.
Here, the adsorption and binding strengths of RE segregants at
prismatic grain surfaces are determined by first-principles
calculations. The adsorption of three rare earths (La, Gd, and Lu) is
expected to be distinctly different at the predicted adsorption sites,
and this is confirmed by atomic-resolution scanning transmission
electron microscopy images. This combination of theory and experiment
provides a basis for understanding the adsorption behavior of RE
elements in silicon nitride ceramics.