Studies of the EPR parameters and tetragonal distortion for the Cu2+ center in aluminium oxide

The electronic paramagnetic resonance (EPR) parameters (g factor gi, and hyperfine structure constants Ai, with i = || and ⊥) and tetragonal distortion of the Cu2+ center in Al2O3 are unified interpreted from the perturbation formulas for a 3d9 ion in tetragonally elongated octahedral. In the calculations, the impurity Cu2+ is found to occupy the host trigonally-distorted octahedral Al3+ site with the tetragonal elongation distortion due to the Jahn–Teller effect, despite the original trigonal distortion of the host cation site. The contributions to EPR parameters from both the spin–orbit coupling of the central ion and that of the ligands are taken into account. The defect structure of the Cu2+ center (characterized by the relative tetragonal elongation ratio η ≈ 4.3% along the C4 axis) was determined from the calculation. Furthermore, the calculated results agree well with the experimental data and need fewer adjustable parameters than the previous studies.