Localization of Fe3+ impurities in kyanite by EPR

An electron paramagnetic resonance (EPR) study of Fe3+ centers in kyanite A lSi2O5 has been performed on a natural blue single crystal at 34.40 GHz. Th ree Fe3+ centers have been observed. One of them, arising from 10% of the F e3+ amount, presents weak signals and few resonance lines inside Kramers do ublets, the weakness of the signals and the high value of the zero-field sp litting between Kramers doublets allow only the determination of the second -order parameters of the spin Hamiltonian. For the two other centers all se cond- and fourth-order parameters are determined. The comparison of the pse udo-symmetries of the fourth-order parameters between EPR results and cryst al field calculation does not allow one to define the location of all Fe3centers at Al octahedra. It is proved that Fe3+ is partly located at Al-l p osition (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 limit ation of the pseudo-symmetry method.