Electrical and optical properties of single crystalline α-Al2O3 doped with nickel

Electrical conductivity measurements, together with emf measurements, of partially compensated Al2O3 containing Fe, Ni, and Mg, indicate that Ni, substituting for Al, is an acceptor with a level of 2.46 eV above the valence band if a large polaron model applies, and 2.57 eV - H(mu-h) above the valence band if a small polaron applies. These results were obtained after a high temperature anneal in atmospheres having different oxidizing power; the results are interpreted on the basis of a detailed, point-defect model.