Zr segregation and associated Al vacancies in alumina grain boundaries

Abstract

Segregated dopants at grain boundary dramatically change the material’s mechanical and electrical properties. The knowledge of the behavior of these dopants are therefore key for further material developments. Here, a Zr doped alumina (Al₂O₃) bicrystal was fabricated and the atomic structure of the grain boundary was characterized using scanning transmission electron microscopy (STEM). Zr was found to segregate to specific sites along the grain boundary, which was neighbored by Al columns of weak image intensity. First principles calculations and static lattice calculations revealed that the charge compensating Al vacancies are most stable in Al columns neighboring the location of the Zr sites. Multi-slice simulations of STEM images confirmed that Al columns containing vacancies exhibit a reduction in image intensity. These results indicate that associated Al vacancies strongly influence its atomic site segregation behavior of Zr.