Phase Transitions and Antiferroelectrivity in BiFeO3 from Atomic Level   Simulations
  The structural and polar properties of BiFeO3 at finite temperature are investigated using an atomistic shell model fitted to first-principles calculations. Molecular Dynamics simulations show a direct transition from the low-temperature R3c ferroelectric phase to the Pbnm orthorhombic phase without evidence of any intermediate bridging phase between them. The high-temperature phase is characterized by the presence of two sublattices with opposite polarizations, and it displays the characteristic double-hysteresis loop under the action of an external electric field. The microscopic analysis reveals that the change in the polar direction and the large lattice strains observed during the antiferroelectric-ferroelectric phase transition originate from the interplay between polarization, oxygen octahedron rotations and strain. As a result, the induced ferroelectric phase recovers the symmetry of the low temperature R3c phase. 
M. Graf, M. Sepliarsky, S. Tinte, and M.G. Stachiotti
cond-mat.mtrl-sci