Electron paramagnetic resonance investigations of  -Al₂O₃powders doped with Fe³ ions: experiments and simulations

Abstract

Electron paramagnetic resonance (EPR) of Fe 3+ ions in Al 2 O 3 is studied in powder samples prepared by different routes and/or modified by thermal or mechanical treatments, with different doping levels and grain sizes. The measurements are performed in various frequency bands (S, X, K, Q and W) and with bimodal detection in X-band. Simulations of the spectra are achieved with a code designed for computing EPR powder spectra described by any spin Hamiltonian including second-, fourth-and sixth-order ZFS terms (S 7/2). The linewidths, intensities and lineshapes are accounted for. The lineshape is Gaussian at low Fe 3+ concentration whereas it is Lorentzian for higher concentration. The linewidths are interpreted as the superimposition of three main contributions: intrinsic linewidth, dipolar broadening and broadening due to lattice imperfections. The latter is tentatively interpreted in terms of quadrupolar spin Hamiltonian parameter distributions treated using firstorder perturbation theory. Whatever the sample, only the b 2 2 spin Hamiltonian parameter is found to be distributed around a mean zero value which corresponds to rhombic distortions. Angle and bond length distributions are tentatively extracted from the b 2 2 distributions which gives some insight into the local order around the spin probe in relation to the preparation and treatment of the samples.

Hybrid electron spin resonance and whispering gallery mode resonance spectroscopy of Fe3+in sapphire

“…12,13,18,19 Three levels exist at zero applied magnetic field, with the dependence of these levels on a dc magnetic field described by the following Hamiltonian:…”

The thermally induced transformation of pseudoboehmite gels—a comparison of the effects of corundum seeding and iron doping

“…The asymmetric resonance at g ∼ 4.3 due to Fe 3+ has become smaller and resonances at g ∼ 13, 5.6 and 2 have now become characteristic. This triple of EPR signals is an X-band fingerprint of Fe 3+ incorporated into corundum [22][23][24] (see also Fig. 9a and f).…”

“…8b) has to be taken into account. As could be shown by spectra simulations 20,22 Fe 3+ resonances at g ∼ 4.3 become narrower if the co-ordination polyhedra show stronger distortions. In the case of aluminas studied here, the transformation from pseudoboehmite (cf.…”

“…10. As Buzare et al 22 have demonstrated, annealing the original sample Alcoa CT 3000 SG results in a less distorted corundum powder. Wet milling of this Alcoa corundum charge, i.e., formation of a suspension of even smaller corundum grains, leads to a further remarkable distortion of the initial corundum lattice.…”

“…Differences in the line width result from magnetic interactions in the Fe 3+ -doped samples. 22,25 The high sensitivity of the Fe 3+ EPR pattern to changes in the distorted corundum lattices also allows a characteri- sation of the ␣-Al 2 O 3 seeds used here (Fig. 10).…”