ESR spectrum of Fe+3 in topaz (Al2SiO4F2) has been investigated at X- and K-band frequencies. The spectrum, in addition to large zero-field splitting, also shows well-resolved h.f.s. due to 19F at some orientations. The spin-Hamiltonian parameters, which include b21 and b41, are given in the text. The spectrum has been interpreted to originate from Fe+3 impurity located at Al+3 sites. The implications of these results are considered briefly. The results of the analysis of the h.f.s. are to be published in the near future.
ESR spectra of Fe+3 in andalusite have been investigated at X- and K-band frequencies at room temperature. They have been interpreted on the assumption that Fe+3 occupies the two inequivalent Al+3 sites in andalusite. The spectra show large zero-field splitting. The constants of the conventional orthorhombic spin Hamiltonian which fit the spectra are as follows: for site I: b20 = 15.0 ± 0.1 kG, b22 = 5.0 ± 0.1 kG, and isotropic g = 2.001 ± 0.002; for site II: b20 = 20.1 ± 0.1 kG, b22 = 0.075 ± 0.010 kG, and isotropic g = 2.004 ± 0.0005. A study of the intensities of ESR signals due to site I follow a pattern predicted by theory. The implications of these results are considered briefly.
The paramagnetic resonance spectra of W+ and Fe3+ in natural crystals of the mineral sillimanite have been investigated. The chromium results can be interpreted with a spin Hamiltonian having axial and rhombic terms. Four magnetically inequivalent (directionally) sites (Site I) are observed, with parameters g 1 = 1.975, 911 = 1.963, B: = 6.91, and Bi = 3.77 GHz. The iron results have been interpreted on the assumption that Fe3+ occupies the two crystallographically inequivalent A13+ sites in the sillimanite, Site I1 having tetrahedral coordination and Site 111 octahedral coordination. The constants of the conventional orthorhombic spin Hamiltonian are as follows, Site 11: B, O = 1.74 GHz, B; = = 1.62 GHz, Bi = 0.0 GHz, B: = 0.0 GHz, B: = 0.0 GHz, and g, = gar = gz = 2.004; Site 111: B: = 11.8 GHz, B; = 4.04 GHz, B: = 0.37 GHz, S i = 0.09 GHz, and g2 = g, = = g, = 2.004. A comparison of the results for the octahedrally coordinated sites in the three polymorphs kyanite, andalusite, and sillimanite is made. Die EPR-Spektren von W + und Fe3+ in naturlichen Kristallen des Minerals Sillimanit aurden untersucht. Die Ergebnisse an Chrom konnen mit einem Spin-Hamiltonian mit axialen und rhombischen Termen interpretiert werden. Vier magnetisch nichtaquivalente (Richtung) Pliitze (Platz I) werden beobachtet, mit Parametern g 1 == 1,975, 911 = 1,963, Bi = 6,91 und B; = 3,77 GHz. Die Ergebnisse a n Eisen werden mit der Annahme erklart, daB Fe3+ die beiden kristallographisch inaquivalenten A13 k-P1atze in Sillimanit -Platz I1 hat tetraedrische und Platz 111 oktaedrische Koordinationbesetzt. Die Konstanten des konventionellen rhombischen Spin-Hamiltonians sind fur Platz I1 : Bl = = 1,74 GHz, BZ = 1,62 GHz, B: = 0,O GRz, B4 = 0,O GHz, Bi = 0,O GHz und gz = = g, = gr = 2,004; fur PlatzIII: B, O = 11,s GHz, Bi = 4,04 GHz, Bi = 0,37 GHz, B: = = 0,09 GHz und g , = gy = gz = 2,004. Ein Vergleich der Ergebnisse fur die oktaedrisch koordinierten Platze wurde fiir die drei Polymorphe Cyanit, Andalusit und Sillimanit durchgefiihrt.
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