Investigations on Bi25FeO40 Powders Synthesized by Hydrothermal and Combustion-like Processes

Abstract.

J. Solid State Chem. 217 (2014) 50–56. (DOI: 10.1016/j.jssc.2014.05.006).

The syntheses of phase−pure and stoichiometric iron sillenite (Bi25FeO40) powders by a hydrothermal (at ambient pressure) and a combustion−like process are described. Phase−pure samples were obtained in the hydrothermal reaction at 100 °C (1), whereas the
combustion−like process leads to pure Bi25FeO40 after calcination at 750 °C for 2 h (2a). The activation energy of the crystallite growth process of hydrothermally synthesized Bi25FeO40 was calculated as 48(9) kJ mol−1. The peritectic point was determined as 797(1) °C. The optical band gaps of the samples are between 2.70(7) eV and 2.81(6) eV. Temperature and field−depending magnetization measurements (5−300 K) show a paramagnetic behaviour with a Curie constant of 55.66·10^−6 m^3·K·mol−1 for sample 1 and C = 57.82·10^−6 m^3·K·mol−1 for sample 2a resulting in magnetic moments of μmag = 5.95(8) μB·mol−1 and μmag = 6.07(4) μB·mol−1. The influence of amorphous iron−oxide as a result of non-stoichiometric Bi/Fe ratios in hydrothermal syntheses on the magnetic behaviour was additionally investigated.