A molecular dynamics method with a reax force fild has been employed to investigate the effect of hydrogen and oxygen vacancy concentrations on the diffusion of oxygen and hydrogen atoms in BaTiO3−xHy□(x-y). The result shows that by using this force fild, the BaTiO3−xHy□(x-y) samples are stable under the condition of x < 0.18. Therefore, the samples have been simulated under conditions of (x-y) <0.15, y < 0.18 and x < 0.18. The results reveal that the dominant diffusion dynamics of hydrogen atoms is the motion between next-nearest neighboring oxygen vacancies in the form of hydride. The diffusion coeffiients and activation energies are evaluated using mean square displacements and Arrhenius plots. The results show that the activation energies of oxide and hydride ions are close together and are in the range of 0.03–0.9 eV and they both decrease by increasing y. The results also show that the pre-exponential factors of hydrogen and oxygen diffusion are in the range of 10−6 to 0.0045 cm2s-1 and 1.7710−6 to 0.0017 respectively
