Where, D is the diffusion coefficient (in m 2 /s), D0 is the maximal diffusion coefficient (at infinite temperature; in m 2 /s), Ea is the activation energy for diffusion (in kJ/mol), T is the absolute temperature (in K) and R ≈ 0.00831 kJ/(mol⋅K) is the universal gas constant. spinel and the corresponding temperature dependent diffusion coefficients have been reported. The authors claimed that the Co diffusion in Al2O3 is limited by the sintering temperature.