Assessment of Self-diffusion Parameters in Alumina Single Crystals

The oxygen ion and aluminum ion self-diffusion parameters in alumina single ciystals were reviewed and assessed, and the diffusion mechanism was analyzed. The results suggest that:(1) In the temperature range from 1770 to 2100 K, oxygen self-diffusion coefficient in single crystal of undoped Al₂O₃ with impurities level of 30×l0^-6~500×l0^-6 (the content of Mg as well as Ti should be less than 30×10^-6), under an oxygen partial pressure less than 1.O× 10⁵ Pa, the formula of self-diffusion confficient and temperature can be obtained. The diffusivity of the oxygen self-diffusion in single crystal of undoped Al₂0₃ is insensitive to the variation of oxygen partial pressure and the diffusion direction. (2) In the temperature range from 1943 to 2178 K, aluminum ion diffusion coefficient in polycrystalline aluminum oxide is about 10^-15 to 10^-14 m²/s, the activation energy is about 477 kJ/mol. (3) The major impurity species in Al₂O₃ single crystal are TiO₂ and MgO. Doping with titania will decrease oxygen self-diffusivity and doping with magnesium will increase oxygen self-diffusivity. Since the contents of other impurity species dissolved in Al₂O₃ are low, the influence of their presence on the oxygen self-diffusivity is not of significance. (4) The diffusion of aluminum and oxygen ions occurs through a vacancy mechanism.