Studies of EPR g factors of the isoelectronic 3d3 series Cr3+, Mn4+ and Fe5+ in SrTiO3 crystals

The g-shifts Δg(=g−gs, where gs≈2.0023 is the free-ion value) of the isoelectronic 3d3 series Cr3+, Mn4+ and Fe5+ in SrTiO3 crystals are calculated from the high-order perturbation formula based on the cluster approach for 3d3 ion in cubic octahedral site. The formula includes not only the contribution from the crystal-field (CF) mechanism, but also that from the charge-transfer (CT) mechanism (which is omitted in the CF theory). From the calculations, it is found that the contribution ΔgCT from the CT mechanism in sign is contrary to the corresponding ΔgCF from the CF mechanism and the relative importance of CT mechanism (characterized by |ΔgCT/ΔgCF|) increases with the increasing valence state (and hence the atomic number) of 3d3 ion. The positive g-shift Δg of SrTiO3:Fe5+ is due mainly to the contribution of CT mechanism. So, for the explanations of g factors of the high valence state 3dn ions (e.g. Mn4+ and Fe5+) in crystals, the contributions from both CF and CT mechanisms should be taken into account.