Nonstoichiometric, Rutile-Type, Solid Solutions in the FeIIF2–FeIIIOF System

Solid solutions of the form FeII(1-x)FeIIIxOxF2-x have been synthesized by the reaction of FeF2 with FeOF in a sealed platinum tube at 850°C. Careful electron probe microanalysis and X-ray powder diffraction have determined the existence of two distinct solid solution regions extending from 0x0.08 at the FeIIF2 end and from 0.71x1 at the FeIIIOF end with a miscibility gap from 0.08x0.71. Electron diffraction experiments have revealed the presence of characteristic diffuse intensity distributions for samples within either solid solution region. Plausible explanations for the observed diffraction phenomena, based upon crystal chemical and bond length–bond valence arguments, are provided.