Raman spectroscopy of single-domain multiferroic BiFeO3

We report the investigation of polarized Raman spectroscopy of multiferroic bismuth ferrite (BiFeO3) from 81-273 K, using a ferroelectric/ferroelastic single-domain crystal with an as-grown pseudocubic (pc) (100)(pc)-oriented surface, compared with (001)(pc) thin film, grown by pulsed laser deposition. The polarized Raman spectra of the single crystal taken at different crystallographic orientations agree with the rhombohedral crystal structure with C-3v point group, whereas the (001)(pc) thin film shows monoclinic structure, contrary to the bulklike rhombohedral and tetragonal structures reported earlier, but consistent with the recent synchrotron radiation studies. Earlier Raman scattering measurements on single crystals violated theoretical predictions. This may be due to mechanical polishing, which allows forbidden E (LO) scattering [J.F. Scott, J. Chem. Phys. 48, 874 (1968); 49, 98 (1968)]. All of the different phonon vibrations (A(1) and E modes) in the single crystal have unambiguously been assigned.