57Fe Mössbauer and Mo K-EXAFS Investigations of MoxFe3-xO4, an Interesting Mixed-Valent Oxide System
✍ Scribed by L. Bouet; Ph. Tailhades; A. Rousset; K.R. Kannan; M. Verelst; G.U. Kulkarni; C.N.R. Rao
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 284 KB
- Volume
- 102
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
Ferrites of the formula (\mathrm{Mo}{4} \mathrm{Fe}{3-}, \mathrm{O}{4}), prepared by a soft-chemistry route, show mixed valence states of both iron and molybdenum cations. Mössbauer studies show that (\mathrm{Fe}^{2+}) and (\mathrm{Fe}^{3+}) ions are present on hoth the (\mathrm{A}) and (\mathrm{B}) sites, giving (\mathrm{Fe}) an average oxidation state between (2+) and (3+). Molybdenum is present in the (3+) and the (4+) states on the (B) sites. The presence of Mo in the (3+) state has been eslablished by determining the (\mathrm{Mo}^{3+}) - (\mathrm{O}) distance ((2.2 \AA)), for the first time, by Mo K-EXAFS. The mixed valence of (\mathrm{Fe}) on both the (\mathrm{A}) and (\mathrm{B}) sites and of (\mathrm{Mo}) on the (\mathrm{B}) sites is responsible for the fast electron transfer between the cations. All the Mössbauer parameters including the line width show a marked change at a composition ((x \approx 0.3)) above which the concentration of (\mathrm{Fe}{A}^{2+}) increases rapidly. (1) ({993) Academic Press, Inc.