Atomic displacements in BiFeO3 as a function of temperature: neutron diffraction study

The parameters of the crystal structure of BiFeO3, described within the space group R3c, have been determined by high‐resolution neutron powder diffraction for temperatures from 293 to 923 K. It was found that there is a local minimum for the rhombohedral angle αrh, near the Néel temperature TN≃ 640 K, a gradual rotation of the FeO6 octahedra and an increase of the Fe—O—Fe angle. The displacement of the Bi3+ ions from the FeO6 octahedra which influence the electric polarization decreases with temperature. One of the Bi—Fe distances also has a local maximum near TN. The atomic vibrations of Bi3+ and O2− ions show a significant anisotropy.