Kationenverteilung und magnetische Ordnung in den Rutilen (Fe_0,5Ta_0,5)O₂ und (Fe_0,45Nb_0,53)O₂

The cation distribution of the compounds (Fe_0,5Ta_0,5)O₂ and (Fe_0,45Nb_0,53)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 AO₂. 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 (Fe_0.5Ta_0.5)O₂ is of MnF₂-type, whereas (Fe_0.45Nb_0.53)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.