The Defect Structure of Unintentionally Doped α-Al2O3 Crystals

Electrical conductivity and the ionic and electronic transference numbers were determined for two types of unintentionally doped single crystalline sapphire for current directions perpendicular to the r plane (1102). One was acceptor dominated and the other was initially donor (H_i^x) dominated, changing to acceptor domination after a prolonged anneal at 1600°C. The positions of the electronic energy levels of dominant impurities and the constants regulating the oxidation-reduction of these impurities and of pure Al₂O₃ are determined. The latter shows a discrepancy with an expression reported previously.