Temperature-dependent Fe-57 Mossbauer spectroscopy and local structure of the mullite-type Bi-2(FexGa1-x)(4)O-9 (0.1 <= x <= 1) solid solution

Abstract

The Bi-2(FexGa1-x)(4)O-9 oxide solid solution possessing a mullite-type structure has been investigated by Fe-57 Mossbauer spectroscopy in dependence of composition (0.1 <= x <= 1) and temperature (293 <= T/K <= 1073). The spectra have been fitted with two doublets for tetrahedrally and octahedrally coordinated high-spin Fe3+ ions, respectively. The experimental areas of the subspectra were used to determine the distribution of iron on the two inequivalent structural sites. The fraction of iron cations occupying the octahedral site is found to increase with decreasing Fe content and the cation distribution is almost independent of temperature. The unusual temperature dependence of the quadrupolar splitting, QS, observed for the octahedral site with dQS/dT > 0 is discussed in connexion with structural data for Bi2Fe4O9. The temperature dependence of Mossbauer isomer shifts and signal intensities is examined in the context of local vibrational properties of iron on the two inequivalent sites of the mullite-type lattice structure. (C) 2013 Elsevier Ltd. All rights reserved.