Defect model and spin-Hamiltonian parameters for the tetragonal Nd3+ center in the tetragonal phase of SrTiO3 crystal

The spin-Hamiltonian parameters (g factors g(parallel to), g(perpendicular to) and hyperfine structure constants (143)A(parallel to), (143)A(perpendicular to), (145)A(parallel to) and (145)A(perpendicular to)) of the tetragonal Nd3+ center in the low-temperature (T approximate to 4.2 K) tetragonal phase of SrTiO3 are calculated from a diagonalization (of energy matrix) method. In the method, the Zeeman and hyperfine interaction terms are attached to the conventional Hamiltonian and a 52 x 52 energy matrix concerning the ground term H-4(J) (J=9/2, 11/2, 13/2, 15/2) is constructed. The Nd3+ center is attributed to Nd3+ occupying the 12-fold coordinated Sr2+ site in SrTiO3. Differing from the defect model assumed in the previous paper that the tetragonal distortion of this Nd3+ center is due to the association of one interstitial oxygen ion at a nearest neighborhood of Nd3+ and the Nd3+ displacement Delta z along C-4 axis, we suggest that it is due to the distortion of SrTiO3 lattice in the tetragonal phase. The calculated g factors g(parallel to) and g(perpendicular to) show good agreement with the experimental values, suggesting that our defect model of Nd3+ center in SrTiO3 is reasonable. The experimental hyperfine structure constants were not reported and so our calculated results remain to be checked by EPR experiment. (C) 2010 Elsevier B.V. All rights reserved.