Electron Spin Resonance of Cr³⁺ Ions Coupled with Oxygen Vacancies in Rutile

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Paramagnetic resonance of Cr³⁺ spins in TiO₂ single crystals were investigated in detail and two sets of weak absorption signals were observed in addition to usual Cr³⁺ resonance lines. By analysing both the directions of the local symmetry axes and the magnitude of spin Hamiltonian parameters D and E of these two groups I and II, it is concluded that these resonances come from substitutional Cr³⁺ spins coupled with the second and the third neighbor oxygen vacancies respectively. Spin Hamiltonian parameters determined for each group are given by
Group I, g=1.98±0.005, D=5.10±0.10 GHz, E=−1.41±0.05 GHz
Group II, g=1.98±0.005, D=−16.5±1.0 GHz, E=−3.9±0.5 GHz.