EPR parameters and defect structures of the off-center Ti3+ ion on the Sr2+ site in neutron-irradiated SrTiO3 crystal

The EPR parameters (g factors and hyperfine structure constants A) for the tetragonal Ti3+ center in cubic phase and the rhombic Ti3+ center in tetragonal phase in the neutron-irradiated SrTiO3 crystals are calculated from the third-order perturbation formulas of EPR parameters for d1 ions. These low-symmetry Ti3+ centers in both phases of SrTiO3 are due to the Ti3+ ion at “off center” on the Sr2+ site. From the calculation, the defect models (including the direction and magnitude of the Ti3+ off-center displacement) of the two Ti3+ centers in SrTiO3 are estimated and the EPR parameters of both Ti3+ centers are reasonably explained on the basis of the defect models. The results are discussed.