Fe- and Cr-substituted mullites: Mössbauer spectroscopy and rietveld structure refinement
Abstract
Fe-substituted mullite samples Al 4.5-yFe ySi 1.5O 9.75 (y = 0.25 and 0.50) have been prepared using a sol-gel route involving Si and Al alkoxides and iron nitrate as precursors. Mössbauer spectroscopy reveals the presence of three different Fe(III) sites but does not allow to conclude concerning the ion environments, tetrahedral or octahedral. Rietveld refinements reveal that Fe ions are distributed between octahedral and tetrahedral positions, the proportion of octahedral iron increasing from y = 0.25 to y = 0.50. On the other hand, for Cr-substituted mullite, Cr ions arc mainly located on octahedral positions. This difference between Fe and Cr has been attributed to the fact that Cr shows a clear trend to occupy octahedral sites compared to Fc and that it is incorporated inside the mullite structure only at high temperature.
- Publication:
-
Solid State Sciences
- Pub Date:
- July 1999
- DOI:
- 10.1016/S1293-2558(00)80080-1
- Bibcode:
- 1999SSSci...1..257P