Investigations of the Defect Structure for Cu2+ in SrLaAlO4

The defect structure for Cu 2+ in SrLaAlO 4 is theoretically investigated by the perturbation formulas of the spin Hamiltonian parameters (g factors g ‖ , g ⊥ and the hyperfine structure constants A ‖ and A ⊥ ) for a 3d 9 ion in tetragonally elongated octahedra. Based on these studies, the tetragonal center may be attributed to Cu 2+ occupying the host Al 3+ site, associated with one hole delocalized at the four oxygen ligands in planar coordination. Furthermore, the four Cu,O bonds (perpendicular to the four-fold axis) are found to suffer an outward stretch of about 0.06 Å due to (i) the local tenseness in this plane, arising from the size mismatching substitution of the smaller Al 3+ by the larger Cu 2+ and (ii) the weaker electrostatic attraction of the less charged Cu2+ acting upon the four oxygen ions containing the delocalized hole. The calculated spin Hamiltonian parameters agree well with the experimental data. The defect structure of this center is discussed.