Investigations of EPR parameters for Cr3+ and Mn4+ ions in anatase (TiO2) crystals

The electron paramagnetic resonance (EPR) parameters (g factors g(parallel to), and g(perpendicular to), and zero-field splitting D) of 3d(3) ions Cr3+ and Mn4+ at the tetragonal substitutional site of anatase (TiO2) crystals are calculated from the complete high-order perturbation formulas based on the cluster approach. These formulas involve not only the widely used crystal field (CF) mechanism, but also the charge transfer (CT) mechanism (which is neglected in the CF theory). The calculated results are in agreement with the observed values. It is found that the relative importance of the CT mechanism for EPR parameters increases with increasing valence state of the 3d(3) ion. So, in the case of 3d(3) ions having high valence state (e.g. Mn4+ ion), a reasonable explanation of EPR parameters should take both CF and CT mechanisms into account.