The atomic and electronic band structures in Ca/Si-doped and Ca/Si/Ti-doped Al2O3 grain boundaries

Grain boundary (GB) segregation plays a crucial role in determining structures, chemistries and resultant properties of polycrystalline ceramic materials. Although GB segregation behaviors of single-element dopants have been extensively investigated, GB segregation in practical polycrystalline ceramics often involves multiple elements. In this study, we conducted experimental investigations to explore the atomic and electronic band structures of Ca/Si-doped and Ca/Si/Ti-doped Al2O3 Σ745̅10 GBs. By employing atomic-resolution scanning transmission electron microscopy combined with density functional theory calculations, we elucidated the interactions between different elements at the GBs. Our findings reveal that Ca and Si were synergistically co-segregated in both GBs, maintaining charge neutrality within the GB core, while the site competition between Ca and Ti occurred in the Ca/Si/Ti-doped GB. Furthermore, valence electron energy loss spectroscopy measurements provided insights into the band gaps of doped GBs, demonstrating that they are dependent on doping species but independent of interactions between different elements.