Modeling of grain-boundary segregation behavior in aluminum oxide

It is believed that the segregation of oversized dopant ions to grain bound aries in Al2O3 hinders grain-boundary diffusion, thereby reducing the tensi le creep rate in this system by similar to 2-3 orders of magnitude. In orde r to explain this improvement in creep behavior, it is helpful to character ize both the effective cation and interstitial volumes at grain boundaries, because the relative openness of some boundary structures suggests a great accommodation of oversized ions. In this study, the boundary volume is det ermined by a spatially local Voronoi construction, which highlights cation (Al3+) substitutional sites as well as large interstitial voids. In particu lar, we examine the spatial distribution of free volume near grain boundari es and, in addition, the dependence of the driving force for segregation on misfit strain in doped Al2O3. We interpret our results in light of recent evidence that selective codoping can provide a more efficient means of fill ing available space near boundaries, thereby further enhancing creep resist ance.