From the perturbation formulas for the EPR ɡ factors g|| and g⊥ of a 3d7 ion in tetragonal octahedral crystal field based on a cluster approach, the geometrical microstructures of tetragonal Co2+-VO centers in KNbO3 and KTaO3 crystals are obtained by fitting the calculated g|| and g⊥ to the observed values. It is found that the Co2+ ion in Co2+-VO centers is displaced away from the oxygen vacancy VO by 0.3 Å in KNbO3 and by 0.29 Å in KTaO3. These results are comparable with those of Fe3+-VO centers in ABO3 perovskite-type crystals obtained fromboth the shell-model simulations and the embedded-cluster calculations, and from theoretical studies of EPR data. The experimental values of g|| and g⊥ for the tetragonal Co2+-VO centers in both crystals are also explained reasonably.
