Phonon anomalies and the ferroelectric phase transition in multiferroic BiFeO3

We report a temperature-dependent Raman scattering investigation of the multiferroic material bismuth ferrite BiFeO3 (BFO). The observed loss of the Raman spectrum at the ferroelectric Curie temperature T-C should be in agreement with a cubic Pm3m structure of the high-temperature paraelectric phase. Surprisingly, the ferroelectric-to-paraelectric phase transition is not soft-mode driven, indicating a nonconventional ferroelectric. Furthermore, our results reveal pronounced phonon anomalies around the magnetic Neel temperature T-N. We tentatively attribute these anomalies to the multiferroic character of BFO.