Stability and defect state of vanadium at BaTiO3 grain boundaries

First-principles and molecular dynamics simulations are used to understand the stability and defect state of vanadium ions at BaTiO3 grain boundaries. Qualitative analysis is performed based on two approaches to approximate polycrystalline grain boundaries. First, stable grain boundaries are modeled to evaluate the defect formation energies of grain boundary sites and bulk sites. Second, amorphous BaTiO3 is used to analyze the relationship between defect structure and stability of vanadium. The electronic states of vanadium atoms in the amorphous state are statistically analyzed to understand the effect of complex structures such as grain boundaries. These results suggest that vanadium acts as a donor at grain boundaries.