EPR Spectrum of Fe3+ in Synthetic Brown Quartz

Abstract

A detailed description is given of the EPR spectrum of Fe³⁺ in synthetic brown quartz (the so‐called $I$ center, presumed to be interstitial). There are three equally populated sites differing only in the orientation of their principal axes, which coincide with the three twofold axes of quartz. The values of the Hamiltonian parameters that fit the data best are: ${\text{g\hspace{0.17em}=\hspace{0.17em}2.0039, C}}_{20}{\text{(≡D)\hspace{0.17em}=\hspace{0.17em}734.3G, C}}_{22}{\text{[≡(6}}^{\text{1\hspace{0.17em}/\hspace{0.17em}2}}{\text{\hspace{0.17em}/\hspace{0.17em}2)|\hspace{0.17em}E\hspace{0.17em}|]\hspace{0.17em}=\hspace{0.17em}401.7G, C}}_{40}{\text{\hspace{0.17em}=\hspace{0.17em}2.52G, C}}_{44}\text{\hspace{0.17em}=\hspace{0.17em}1.40G}$ , where the $C_{\mathrm{lm}}$ are the coefficients of the Racah operators in the Hamiltonian. Lobes of the $V_{22}{\mathrm{,\; V}}_{42}$ , and $V_{44}$ parts of the crystal‐field potential point 0.7°, 29.5°, and 26.8°, respectively, from the optic axis of quartz. The occurrence of irregular off‐axis extrema of the line positions when the magnetic field is directed in the vicinity of the optic axis precludes the assignment of magnetic axes of the paramagnetic center in the usual way. All features of the spectrum are predicted accurately by computer calculations based on the derived Hamiltonian. Although the data are not conclusive evidence, they are believed to be more consistent with an assignment of the $I$ center to a substitutional site.