F. Bernard et al., Cation distribution in a titanium ferrite Fe2.75Ti0.25O4 measured by in-situ anomalous powder diffraction using Rietveld refinement, J SOL ST CH, 141(1), 1998, pp. 105-113
Many ferrites contain different cations with various valence states and loc
ation in the spinel structure. In compounds such as these, only a combinati
on of different techniques such as Mossbauer spectroscopy, IR analysis, and
thermogravimetry allows the distribution of cations to be obtained. For ve
ry complicated distributions, the mathematical decomposition of derivative
thermogravimetric curves (DTG) leading to quantitative distribution is unce
rtain. In this paper, me present an alternative technique based on resonant
diffraction, The anomalous scattering of each cation in the crystalline ma
terial is used to determine its amount and position by Rietveld refinement.
Since the energy for such an anomalous phenomenon is different for each ca
tion, this technique should lead to the cation distribution whatever its co
mplexity. Such a method in which the wavelength has to be varied with a gre
at accuracy requires a synchrotron radiation source. The method has been te
sted in the simple case of titanium ferrites where the valence and location
of the Fe cations can be adjusted through appropriate thermal treatments i
n reducing or oxidizing conditions. The aim of this paper is to validate th
is new method by comparing the cation distribution so obtained with that de
duced from thermogravimetry experiments. In particular, we focus on its abi
lity to distinguish between the different degrees of oxidation of the iron
cations, Three different diffraction patterns have been recorded using the
high-resolution goniometer on the BM02 Beam line at ESRF at the following e
nergies: 7.105 keV, below the adsorption edges of both Fe2+ and Fe3+ cation
s; 7.120 keV, above the absorption edge for Fe2+ cations but below the Fe3 edge and 7.135 keV, above the absorption edges of the Fe2+ and Fe3+ cation
s. (C) 1998 Academic Press.