EPR study ofFe3+in α-quartz: Further lithium-compensated centers

${\mathrm{Fe}}^{3+}$ (S=52) centers in synthetic α-quartz, designated by ${\mathrm{S}}_1^{\prime }$ and ${\mathrm{S}}_1^{\mathrm{″}}$ by previous workers, which are very similar to the previously studied center [${\mathrm{FeO}}_4$/Li${]}_{\mathrm{\alpha }}^0$ (called ${\mathrm{S}}_1$), have been examined at temperatures around 35 K via an X-band electron-paramagnetic-resonance study. Hyperfine signals due to the ${\mathrm{Li}}^7$ nucleus were detected for both centers, establishing their alkali-metal-ion content. The spin-Hamiltonian parameters were determined, allowing for anisotropy of the g factor as well as [g,D,A(${\mathrm{Li}}^7$), P(${\mathrm{Li}}^7$)]-matrix noncoaxiality, and including high-spin terms of the form ${\mathrm{S}}^4$. Evaluation of the results indicates that the lithium 1+ ion is present interstitially near to the substitutional ${\mathrm{Fe}}^{3+}$ ion (located at a ${\mathrm{Si}}^{4+}$ site) on the same crystal twofold axis, for all three centers: ${\mathrm{S}}_1$, ${\mathrm{S}}_1^{\prime }$ and ${\mathrm{S}}_1^{\mathrm{″}}$. The designations [${\mathrm{FeO}}_4$/Li${]}_{\mathrm{\alpha }\prime }^0$ are proposed for the centers ${\mathrm{S}}_1^{\prime }$ and ${\mathrm{S}}_1^{\mathrm{″}}$, respectively. The relative concentrations of these centers appear to depend sensitively on the growth regions within each crystal.