Bi2Fe4O9: Structural changes from nano- to micro-crystalline state

Abstract

Abstract Bi2Fe4O9 was synthesized using a polyol-mediated method. X-ray powder diffraction (XRPD) revealed that the as-synthesized sample is nano-crystalline. During heating, the X-ray amorphous powder transformed into a rhombohedral perovskite-type bismuth ferrate followed by a second transformation into mullite-type Bi2Fe4O9 at higher temperatures. This transformation was studied at in-situ conditions by temperature-dependent XRPD and 57Fe Mössbauer spectroscopy. The 57Fe Mössbauer spectra indicate the existence of two Fe3+ species at two different octahedrally coordinated sites leading to the conclusion that the as-synthesized powder of the polyol synthesis possesses a disordered (Bi1–x Fe x )FeO3 perovskite structure. Rietveld refinements have unambiguously supported this observation and this results suggest that one third of the Bi3+ sites are substituted by Fe3+ representing the initial chemical composition. This study has shown that as-synthesized nano-materials are not always similar to the respective micro-crystalline ones.