Bismuth ferrite

Bismuth ferrite (BiFeO₃, also commonly referred to as BFO in materials science) is an inorganic chemical compound with perovskite structure and one of the most promising multiferroic materials. The room-temperature phase of BiFeO3 is classed as rhombohedral belonging to the space group R3c. It is synthesized in and thin film form and both its antiferromagnetic (G type ordering) Néel temperature and ferroelectric Curie temperature are well above room temperature (approximately 653 K and 1100K, respectively). Ferroelectric polarization occurs along the pseudocubic direction (${\displaystyle \langle 111\rangle _{c}}$ ) with a magnitude of 90–95 μC/cm2.

Bismuth ferrite is not a naturally occurring mineral and several synthesis routes to obtain the compound have been developed.

In the solid state reaction method bismuth oxide (Bi₂O₃) and iron oxide (Fe₂O₃) in a 1:1 mole ratio are mixed with a mortar, or by ball milling and then fired at elevated temperatures. The volatility of bismuth and the relatively stable competing ternary phases Bi₂₅FeO₃₉ (sillenite) and Bi₂Fe₄O₉ (mullite) makes the solid state synthesis of phase pure and stoichiometric bismuth ferrite challenging. Typically a firing temperature of 800 to 880 Celsius is used for 5 to 60 minutes with rapid subsequent cooling. Excess Bi₂O₃ has also been used a measure to compensate for bismuth volatility and to avoid formation of the Bi₂Fe₄O₉ phase.

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