An in situ study of the formation of multiferroic bismuth ferrite using high resolution synchrotron X-ray powder diffraction

The synthesis of multiferroic BiFeO3 has been undertaken in situ using both vacuum and argon atmospheres. We have collected and refined synchrotron X-ray powder diffraction data from pressed pellets of the starting powders of Bi2O3 and Fe2O3 at intervals in the reaction to form the final multiferroic BiFeO3 product. Data were collected at 3-min intervals following as realistically as possible the sintering regimes used in industry. The difference in the transformation temperature of monoclinic Bi2O3 to cubic Bi2O3 was found to be 650 and 700 °C when samples were sintered in a vacuum and argon environments, respectively. It was found that this reaction was 75% complete before the multiferroic product began to form. In both cases it was found that the quantity of Fe2O3 was unaffected by increasing temperature until after the transition of monoclinic to cubic Bi2O3 had reached its maximum value. After this transition the quantities of cubic Bi2O3 and Fe2O3 were found to decrease at very similar rates yielding the final BiFeO3 structure. An SEM study of the bulk microstructure of the BiFeO3 product showed a poor densification due to incomplete reactions between the remaining Bi2O3 and Fe2O3.