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

Abstract

Electron paramagnetic resonance (EPR) of Fe3+ ions in Al2O3 is studied in powdersamples prepared by different routes and/or modified by thermal or mechanicaltreatments, with different doping levels and grain sizes. The measurementsare performed in various frequency bands (S, X, K, Q and W) and withbimodal detection in X-band. Simulations of the spectra are achieved with acode designed for computing EPR powder spectra described by any spinHamiltonian including second-, fourth-and sixth-order ZFS terms (S ≤ 7/2).The linewidths, intensities and lineshapes are accounted for. The lineshape isGaussian at low Fe3+ concentration whereas it is Lorentzian for higherconcentration. The linewidths are interpreted as the superimposition ofthree main contributions: intrinsic linewidth, dipolar broadening andbroadening due to lattice imperfections. The latter is tentatively interpreted interms of quadrupolar spin Hamiltonian parameter distributions treatedusing first-order perturbation theory. Whatever the sample, only theb22spin Hamiltonian parameter is found to be distributed around amean zero value which corresponds to rhombic distortions. Angle andbond length distributions are tentatively extracted from the b22distributions which gives some insight into the local order around thespin probe in relation to the preparation and treatment of the samples.