Electron-Spin Resonances in Reactor-Irradiated Aluminum Oxide

Three prominent paramagnetic absorption systems have been detected in single crystals of α aluminum oxide (Al₂{O}₃$) following reactor irradiation with and without subsequent low-temperature gamma-ray irradiation. The most prominent system has an asymmetric, slightly anisotropic absorption with $g{≈}2.00$, which appears to result from the superposition of components from several paramagnetic centers. A second system consisting of twelve equally intense lines corresponds to a spin-one center in six inequivalent sites whose z axes are perpendicular to the crystal c axis and nearly parallel to rows of O^2- ions. The spin-Hamiltonian parameters for this defect are: gz=2.0105±0.0020, gₓ=gy=2.0190±0.0020, $S=1$, |D|=0.0710±0.0002 cm^-1, and |E|=0.0025±0.0005 cm^-1, where D and E have the same sign. Its spectrum is attributed to an AlO^3- molecular ion in a pair of oxygen sites, formed by a replacement collision. The third system is obtained when a reactor-irradiated crystal of Al₂{O}₃$ is gamma-ray irradiated at 77^∘{}K and measured prior to warming up. It is a three-line system which saturates with gamma-ray dose but whose saturation level increases with reactor dose. This system corresponds to a spin-3/2 center with a symmetry axis parallel to the c axis; its spin-Hamiltonian parameters are: g_∥=2.018±0.002, g_⊥=2.011±0.002, S=3/2, and |D|=0.0373±0.0002 cm^-1. It is attributed to interstitial O⁺ formed from interstitial O⁰ by ionization or hole trapping.