Defect Structure of α‐Al 2 O 3 Doph with Magnesium

The conductivity of single crystals of Al 2 O 3 + Mg and the ionic and electronic transference numbers were measured at high temperatures as a function of orientation, oxygen pressure, and temperature. Optical absorption in the visible range was measured on cooled annealed crystals. The results are interpreted on the basis of a model with either Al i 3‐ or V O as the dominant native defects and lead to expressions for the ionic mobility as a function of T and orientation, and for the position of the Mg Al ’level in the forbidden gap.