Controllable phase evolution of bismuth ferrite oxides by an organic additive modified hydrothermal method

Bismuth ferrite crystallites were synthesized by an organic additive modified hydrothermal method using Fe(NO3)3·9H2O and Bi(NO3)3·5H2O as starting materials with NaOH as the mineralizer. The phase evolution of bismuth ferrites in the process of hydrothermal reactions was controlled by adjusting the process parameters, such as NaOH concentration, reaction temperature and duration time. X-ray diffraction (XRD) analysis indicated that the pure phase of Bi25FeO40, BiFeO3 and Bi2Fe4O9 were synthesized at the temperature of 200 °C for 24 h with NaOH concentration of 2, 5 and 10 M, respectively, with the addition of polyvinyl alcohol (PVA). It was found that the addition of PVA postponed the evolution progress between different phases of bismuth ferrites and widened the individual Bi–Fe oxides existence range of processing parameters. Moreover, the mechanism of forming different bismuth ferrites in the hydrothermal process was investigated and discussed.