The β-to-γ Transition in BiFeO3: A Powder Neutron Diffraction Study

High-temperature powder neutron diffraction experiments are conducted around the reported beta-gamma phase transition (similar to 930 degrees C) in BiFeO3. The results demonstrate that while a small volume contraction is observed at the transition temperature, consistent with an insulator-metal transition, both the beta- and gamma-phase of BiFeO3 exhibit orthorhombic symmetry; i.e., no further increase of symmetry occurs during this transition. The gamma-orthorhombic phase is observed to persist up to a temperature of approximately 950 degrees C before complete decomposition into Bi2Fe4O9 (and liquid Bi2O3), which subsequently begins to decompose at approximately 960 degrees C.