A detailed investigation using variable temperature powder neutron diffraction demonstrates that ${\mathrm{BiFeO}}_3$ undergoes a phase transition from the ferroelectric $\alpha$ phase (rhombohedral, $R3c$) to a paraelectric $\beta$ phase (orthorhombic, $Pbnm$) between $820°\mathrm{C}$ and $830°\mathrm{C}$. Coexistence of both phases over a finite temperature interval, together with abrupt changes in key structural parameters, confirms that the transition is first order. The $\beta$ phase corresponds to a ${\mathrm{GdFeO}}_3$-type perovskite structure.

• Received 4 November 2008

DOI:https://doi.org/10.1103/PhysRevLett.102.027602