Application de la RPE à la localisation des substitutions isomorphiques dans les micas: Localisation du Fe3+ dans les muscovites et les phlogopites

Electron spin resonance spectra attributed to four Fe³⁺ centers designated O_a, O_b, T_a, T_b have been observed in crystals of muscovite and phlogopite. The results are discussed using the spin Hamiltonian

with g_e ～ 2.002. The angular variation of the resonance lines is used to determine the ESR axes of the four different sites. Two species are octahedrally coordinated (O_a and O_b) and are assigned to two different surroundings of Fe³⁺ in the octahedral sheet. The remaining two species (T_a and T_b) may be assigned to the tetrahedral FeO₄. The T_a sites have a symmetry axis lying along one of the FeO bonds. The symmetry axis is created by an excess of negative charge on the oxygen bound to the neighboring tetrahedral substitution. Rhombic symmetry of the T_b sites is due to the presence of fluorine anions substituting some hydroxyl ions. One of the ESR axes is directed toward the fluorine ion.