Atomic and electronic band structures of Ti-doped Al2O3 grain boundaries

Doping is one of the most popular strategies to modify the properties of polycrystalline materials, because the dopants prefer to segregate at the grain boundaries (GBs) and influence the structural and electronic properties of the materials. Understanding how dopants segregate at GBs and how they affect the resultant GB properties are essential. Here, we experimentally characterized the atomic structures and the electronic band structures of Ti-doped Sigma 7{4 (5) over bar 10} and Sigma 7{2 (3) over bar 10} GBs in alpha-Al2O3 by atomic resolution scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDXS) and valence electron energy-loss spectroscopy (EELS). It was found that Ti preferentially segregated at specific atom sites driven by ionic size mismatch between Ti3+ and Al3+, which leads to structural transformations in both GBs. Direct valence EELS measurement revealed the segregation of Ti3+ ions introduces impurity band within the bandgap in Al2O3 GBs. These results provide an in-depth understanding of the local atomic and electronic band structures for Ti-doped GBs. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.