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

An Y-doped ∑7{4510}[0001] Al₂O₃ grain boundary was fabricated by the bicrystal method. The grain boundary segregation structure was studied using atomic-resolution scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. It was found that the atomic structure of the Y-doped grain boundary differs from that of the non-doped grain boundary, indicating that Y doping induced the structural transformation from asymmetrical shape to symmetrical shape in the grain boundary core. Apart from Y, impurities of Ca were also segregated at the grain boundary. Both Y³⁺ and Ca²⁺ are segregated at the same atomic columns in the grain boundary, mainly due to their larger ionic size compared with Al³⁺. In addition, valence electron energy loss spectroscopy measurements indicate that the bandgap energy of the doped grain boundary is about 0.5 eV smaller than that of the pristine grain boundary.