Iron valence in double-perovskite (Ba,Sr,Ca)(2)FeMOO6: isovalent substitution effect
Journal
Journal of Solid State Chemistry
Journal Volume
177
Journal Issue
8
Pages
2655-2662
Date Issued
2004
Author(s)
Abstract
In the Fe-Mo based B-site ordered double-perovskite, A 2FeMoO 6.0, with iron in the mixed-valence II/III state, the valence value of Fe is not precisely fixed at 2.5 but may be fine-tuned by means of applying chemical pressure at the A-cation site. This is shown through a systematic 57Fe Mössbauer spectroscopy study using a series of A 2FeMoO 6.0 [A=(Ba,Sr) or (Sr,Ca)] samples with high degree of Fe/Mo order, the same stoichiometric oxygen content and also almost the same grain size. The isomer shift values and other hyperfine parameters obtained from the Mössbauer spectra confirm that Fe remains in the mixed-valence state within the whole range of A constituents. However, upon increasing the average cation size at the A site the precise valence of Fe is found to decrease such that within the A=(Ba,Sr) regime the valence of Fe is closer to II, while within the A=(Sr,Ca) regime it is closer to the actual mixed-valence II/III state. As the valence of Fe approaches II, the difference in charges between Fe and Mo increases, and parallel with this the degree of Fe/Mo order increases. Additionally, for the less-ordered samples an increased tendency of clustering of the antisite Fe atoms is deduced from the Mössbauer data. © 2004 Elsevier Inc. All rights reserved.
SDGs
Type
journal article