Localization of Fe3+ impurities in kyanite by EPR

Abstract

An electron paramagnetic resonance (EPR) study of Fe" centers in kyanite AISi 2O, has been performed on a natural blue single crystal at 34.40 GHz. Three Fe" centers have been observed. One of them, arising from 10% of the Fe" amount, presents weak signals and few resonance lines inside Kramers doublets, the weakness of the signals and the high value of the zero-field splitting between Kramers doublets allow only the determination of the second-order parameters of the spin Hamiltonian. For the two other centers all second-and fourth-order parameters are determined. The comparison of the pseudo-symmetries of the fourth-order parameters between EPR results and crystal field calculation does not allow one to define the location of all Fei centers at Al octahedra. It is proved that Fe" is partly located at Al l position (25%). For the other observed centers it was not possible to define their location in the structure. This study is a good example of the limitation of the pseudo-symmetry method.