Structural Studies of Bi2(FexAl1-x)4O9 Solid Solutions (0.1≤x≤1.0) Prepared by a Combined Mechanochemical/Thermal Synthesis

Overview & Synopsis

Bi2(FexAl1-x)4O9 solid solutions with 0.1 ≤ x ≤ 1.0 prepared via mechanochemical processing of α-Fe2O3/Bi2O3/Al2O3 mixtures and subsequent annealing have been investigated by X-ray diffraction, Mössbauer spectroscopy, and EDX. A Rietveld refinement was made for the whole range of the solid solutions. The structure is orthorhombic with space group Pbam. Mössbauer spectroscopy reveals paramagnetic behaviour for Bi2(FexAl1-x)4O9 with 0.1 ≤ x ≤ 1.0 at room temperature and indicates significant distortion of the octahedral iron coordination for aluminium-rich mixed crystals. The occupancy of octahedrally and tetrahedrally coordinated sites was determined by Mössbauer spectroscopy and Rietveld analysis. For x ≥ 0.5, the Mössbauer measurements as well as the Rietveld refinements show an almost random distribution of aluminium and iron cations over the two non-equivalent sites, whereas for x < 0.5 a slight preference of iron for the octahedral sites is observed.