No abstract

The cation distribution of the compounds (Fe0.: Tao.5)O 2 and (Feo.45Nbo.53)O2 has been redetermined by the combined use of neutron and X-ray powder diffraction. Analysis of the powder patterns showed that the compounds are isostructural, their structure being of the rutile-type A O 2. The cations are statistically distributed. There exists no partial ordering, neither of Fe and Ta nor of Fe and Nb. Neutron diffraction patterns taken at 4.2 K showed only one magnetic reflection, which is strongly broadened. The magnetic structure of (Feo.sTa0.5)O 2 is of MnF2-type, whereas (Fe0.45Nbo.53)O2 orders in the BEY-structure. Profile analysis of these broadened reflections was carried out with the convolution integral of a Gaussian with a Lorentzian function, from which correlation lengths could be derived.