Mechanism of self-trapped hole motion in corundum crystals

Atomistic simulations of the self-trapped hole equilibrium geometry and migration in a pure corundum crystal have been carried out using the semiempirical method of intermediate neglect of differential overlap and atom-atom potentials, as implemented in the CASCADE code. The activation energies for three different hole-hopping mechanisms are calculated. It is shown that the 60° reorientations of a self-trapped hole and hopping to the nearest O-atom triangle require almost the same activation energy, approximately 0·9 eV, which agrees quite well with the experi-mental value for hole migration of 0·7 eV. A new mechanism of small-polaron motion is suggested.