Additionally, an exponential relation for the diffusion time and temperature was obtained as shown in Figure . The estimated times for 4 oxygen atoms appearing on the surface are 2.40×10 4 ns, 1.56×10 7 ns, and 7.72×10 11 ns (772 s ≈ 0.2 h) at 500 K, 400 K, and 300 K, respectively. From the relation, at 300K, the diffusion time for 3.5 nm is 7.3 h. The diffusion of oxygen is greatly constrained in the latter case, thus difficult to be observed in the time scale of simulations but certainly can occur on the time scale of the experiment.