First-principles simulations and Z-contrast imaging of impurities at <001> tilt grain boundaries in MgO

摘要

First-principles density-functional calculations were used to study the effects of CA impurities on the (Sigma) = 5 (310) <001> tilt grain boundaries in MgO. An equilibrium structure and two metastable structures of the grain boundaries in pure MgO have been established. The calculations further demonstrated that Ca impurities segregate at particular sites in the metastable grain boundary and induce a structural transformation. This result is consistent with atomic resolution Z-contrast imaging. The calculations also found that the impurities at the grain boundaries do not induce states in the band gap. The mechanism of the transformation is also discussed.