An electron diffraction and crystal chemical investigation of oxygen/fluorine ordering in rutile-type iron oxyfluoride, FeOF

Rutile-type iron oxyfluoride, FeOF, has been synthesized by the reaction of FeF3 with Fe2O3 in a sealed platinum tube at 950 degreesC. The compound was previously believed to have a random distribution of oxygen and fluorine anions surrounding each of the Fe3+ cations, In this work, electron diffraction experiments have revealed the presence of a characteristic diffuse intensity distribution in the form of continuous rods of diffuse intensity running along both the [110]* and [1 (1) over bar0]* directions of reciprocal space through the (h+k+1) = odd parent rutile reflections. Fe3+ shifts induced by local O/F ordering are shown to be responsible for the characteristic reciprocal space intensity distribution of this observed diffuse scattering. The continuous < 110 >* rods of diffuse intensity require the existence of orthogonal {110} planes within the parent rutile structure which exhibit long-range, two-dimensional, oxygen/fluorine ordering, but with no correlation from one {110} plane to the next. A crystal chemical explanation is proposed to support this argument. (C) 2000 Academic Press.