Experimental and ab initio study of the nuclear quadrupole interaction of 181Ta-probes in an α-Fe2O3 single crystal

We report perturbed-angular-correlation (PAC) experiments on 181Hf (→181Ta)-implanted corundum α-Fe2O3 single crystal in order to determine the magnitude, symmetry and orientation of the electric-field-gradient (EFG) tensor at Ta donor impurity sites of this semiconductor. These results are analyzed in the framework of ab initio full-potential augmented-plane wave plus local orbital (FP-APW+lo) calculations. This combined analysis enables us to quantify the magnitude of the lattice relaxations induced by the presence of the impurity and to determine the charge state of the impurity donor level introduced by Ta in the band gap of the semiconductor.