Environment of Fe3+ at the M2 and Si sites of forsterite obtained from EPR

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Abstract
Electron paramagnetic resonance of a forsterite Mg2SiO4 crystal doped with 57Fe revealed two strong Fe3+ centers which can be unambiguously assigned to the M2 and Si sites. All the fourth order terms of the spin Hamiltonian were determined for the two centers. It is shown that the local environment of Fe3+ at M2 is distorted without any apparent pseudoaxial symmetry, while the environment of Fe3+ at the Si position exhibits a strong axial distortion along the crystallographic a direction. There is no immediate local charge compensation for the Mg2+ and Si4+ substitution by Fe3+ in the crystal.