Phase Separation of ϵ‐Fe₂O₃ and BaFe₁₂O₁₉ in a Synthesis Combining Reverse‐Micelle and Sol‐Gel Techniques

Abstract

Epsilon iron oxide (ε‐Fe2O3) and magnetoplumbite barium ferrite (BaFe12O19) are well‐known hard ferrites. For one synthesis method of ε‐Fe2O3, combining reverse‐micelle and sol‐gel techniques, Ba ions are used to accelerate the formation of nanorod‐shaped ε‐Fe2O3. On the other hand, in synthesis of BaFe12O19 both Ba and Fe ions are used to form the final product. However, the coexistence of these two ferrites has not been reported by any synthesis. Herein, we investigated the effect of Ba ions on the final product for the synthesis combining reverse‐micelle and sol‐gel techniques. At a low Ba ion ratio of [Ba]/[Fe]=0.2, ε‐Fe2O3 nanorods are formed, while at higher Ba ion ratios ([Ba]/[Fe]= 0.4, 1, 2), BaFe12O19 appears. The phase diagram at 1000 °C shows that at a Ba ion ratio of [Ba]/[Fe]= 1, the ratio of ε‐Fe2O3 and BaFe12O19 is almost 1:1. The diagram shows intermediates between these two phases do not form, indicating a phase separation of ε‐Fe2O3 and BaFe12O19. During the sintering process of this synthesis, initially perovskite‐type Ba2Fe2O5 and γ‐Fe2O3 nanoparticles form. Then, in areas where γ‐Fe2O3 nanoparticles are gathered around Ba2Fe2O5 and react, BaFe12O19 is formed, whereas in areas lacking Ba2Fe2O5, ε‐Fe2O3 nanorods are formed within Ba‐ion containing silica glass.