EPR study ofFe3+in α-quartz: The sodium-compensated center

Electron paramagnetic resonance studies of a sodium-compensated ${\mathrm{Fe}}^{3+}$ (S=5/2) center in synthetic iron-doped α-quartz have been carried out at ∼20 K. The center is found to have only ${\mathit{C}}_1$ symmetry at this temperature. The spin-Hamiltonian parameters were determined, allowing anisotropy of the g factor, as well as [g,D] matrix noncoaxiality, and including high-spin terms of the form ${\mathit{S}}^4$. We consider the center to consist of an ${\mathrm{Fe}}^{3+}$ ion occurring substitutionally at a ${\mathrm{Si}}^{4+}$ site, with charge compensation provided by an interstitial sodium ion situated nearby (off the crystal twofold axis threading the site). The designation [${\mathrm{FeO}}_4$/Na${]}^0$ is proposed for the center.