Electron paramagnetic resonance of Fe3+ in diopside and spodumene

A study of the EPR spectrum of Fe³⁺ in diopside CaMg(SiO₃)₂ and spodumene LiAl(SiO₃)₂ has been made. It permits the calculation of all the constants of the spin Hamiltonian. We show that the pseudosymmetry axes of the fourth order tensor of the spin Hamiltonian are the same as the axes of the immediate environment of the Fe³⁺. From the fourth order constants of the spin Hamiltonian it is possible to obtain qualitative information about the Fe³⁺ environment. In both crystals, the Fe³⁺ is in the M 1 site. We show that the M 1 site is smaller and more distorted in spodumene than in diopside, and that in spodumene there is large tetragonal distortion along the $\text{M\hspace{0.17em}1–01′}$ direction. It is seen that the information we obtain agrees very well with the crystallographic results.