Atomic structures of Ti‐doped α‐Al2O3 Σ13 grain boundary with a small amount of Si impurity

Doping is a fundamental technique to control sintering of α‐Al2O3, and many types of elements have been used to control grain growth and material properties. Such dopants tend to be concentrated at the grain boundaries and modify grain boundary properties. It is therefore important to investigate the variation of grain boundary atomic structures induced by additives. However, in the sintering process it is difficult to prevent small amounts of unintentional impurity (such as Si), and the potential influence of additives and impurities on the grain boundary structure should be taken into account. Here we show that two types of grain boundary atomic structures are formed in a Ti‐doped Σ13 [12¯10]/(101¯4) α‐Al2O3, which has been determined by atomic‐resolution scanning transmission electron microscopy. Combining with atomic‐scale spectroscopic analyses, we elucidate that the local concentration of Si impurities significantly alters the grain boundary atomic structures and the valence state of Ti additives. The present results suggest that the subtle change in concentrations of both additives and impurity should have a strong impact on sintering processes and resultant properties in α‐Al2O3.