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 C 4 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.

中文翻译：

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氧化铝中Cu2+中心的EPR参数和四方畸变研究

电子顺磁共振 (EPR) 参数（g 因子 gi 和超精细结构常数 Ai ，其中 i = || 和 ⊥）和 Al2O3 中 Cu2+ 中心的四方畸变从四方拉长的 3d9 离子的扰动公式中统一解释八面体。在计算中，发现杂质 Cu2+ 占据主体三角扭曲的八面体 Al3+ 位点，由于 Jahn-Teller 效应导致四方伸长变形，尽管主体阳离子位点的原始三角变形。考虑了中心离子的自旋轨道耦合和配体的自旋轨道耦合对 EPR 参数的贡献。通过计算确定了 Cu2+ 中心的缺陷结构（以沿 C 4 轴的相对四方伸长率 η ≈ 4.3% 为特征）。此外，