Electron paramagnetic resonance spectra of Fe2+ and Fe3+ ions in SrO: evidence for off-centre displacement of Fe2+ ions

Abstract

The electron paramagnetic resonance (EPR) spectra of Fe2+ and Fe3+ ions in single crystals of SrO are reported. Fe3+ ions occupy sites of orthorhombic symmetry and their EPR spectra have been fitted with an S=5/2 spin-Hamiltonian in which the dominant second-order terms have coefficient values of B20=(884.7+or-0.3)*10-4 cm-1 and B22=(-422.0+or-0.5)*10-4 cm-1. Fe2+ ions occur at sites of trigonal symmetry, and the single observed resonance line may be described by a spin-Hamiltonian with S'=1/2, gperpendicular to =0, g/sub ///=3.992+or-0.005 and A/sub ///(Fe57)=30.2+or-0.6*10-4 cm-1. Variable temperature experiments indicate that the Fe2+ resonance occurs between the two levels of a doublet lying 12+or-1 cm-1 above a ground state singlet. A lattice distortion calculation, based on a model of polarisable point ions, and which incorporates the crystal field stabilisation energy, is applied to the cases of Fe2+ and Mn2+ ions substituted into alkaline earth oxide host lattices. The calculation is used to support an interpretation of the spectroscopic data for SrO:Fe in which the trigonal Fe2+ site arises from an off-centre displacement of the Fe2+ ion along a (111) axis.