Temperature dependent Fe 2+ →Fe 3+ electron delocalization in ilvaite

The observation of an “electron hopping phenomenon” in ilvaite, CaFe 2 2+ Fe3 + Si 2 0 8 (OH), has been made by previous workers. The effect of temperature on Fe 2+ →Fe 3+ electron delocalization in ilvaite is closely investigated in the present study. Mössbauer spectra of a suite of naturally‐occurring ilvaites were recorded over a range of temperatures, 80K to 575K. Delocalization is readily confirmed in the spectra with appearance of species with parameters intermediate to Fe 2+ and Fe 3+ . Contrary to prior investigations, five doublets are required to fit the spectra and are assigned to Fe 3+ (A), Fe 2+ (A), Fe 2+ (B), and Fe 2+ (A)→Fe 3+ (A) ∥c and ⊥c. Doublets associated with delocalization are resolved at 80K and preclude the use of an order‐disorder transition model. We propose a thermal activation model and draw some implications for geophysical applications.