Raman spectroscopy of single-domain multiferroic ${\text{BiFeO}}_3$

We report the investigation of polarized Raman spectroscopy of multiferroic bismuth ferrite $\left({\text{BiFeO}}_3\right)$ from 81–273 K, using a ferroelectric/ferroelastic single-domain crystal with an as-grown pseudocubic (pc) ${\left(100\right)}_{\text{pc}}$-oriented surface, compared with ${\left(001\right)}_{\text{pc}}$ 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 $C_{3\text{v}}$ point group, whereas the ${\left(001\right)}_{\text{pc}}$ 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); J. F. Scott, J. Chem. Phys.49, 98 (1968)]. All of the different phonon vibrations ($A_1$ and $E$ modes) in the single crystal have unambiguously been assigned.

Figure 1

(Color online) Polarized Raman spectra of single-domain ${\text{BiFeO}}_3$ single crystal; (a) scattering along $\text{Z}\left(\text{XX}\right)\overline{\text{Z}}$ and $\text{Z}\left(\text{XY}\right)\overline{\text{Z}}$ polarization configurations at 81 K. The insets show magnification of 70–100 wave numbers and 250–325 wave numbers; (b) along $\text{Z}\left(\text{XY}\right)\overline{\text{Z}}$ and $\text{Y}\left(\text{ZX}\right)\overline{\text{Y}}$ configurations at room temperature. Inset shows a multiphonon peak observed at $\sim 1250{\text{cm}}^{-1}$ in $\text{Z}\left(\text{XX}\right)\overline{\text{Z}}$ and $\text{Z}\left(\text{XY}\right)\overline{\text{Z}}$ configurations.

Figure 2

(Color online) Polarized Raman spectra of single-domain ${\text{BiFeO}}_3$ single crystal in $\text{Y}\left(\text{ZZ}\right)\overline{\text{Y}}$ scattering configuration at 300 K. The spectrum along $\text{Z}\left(\text{XX}\right)\overline{\text{Z}}$ direction at 81 K is given to distinguish between $A_1$ (LO) and $A_1$ (TO) modes.

Figure 3

(Color online) Temperature-dependent polarized Raman spectra of as-grown single-domain ${\text{BiFeO}}_3$ single crystal from 81–273 K at different scattering configurations; (a) along $\text{Z}\left(\text{XX}\right)\overline{\text{Z}}$ and (b) $\text{Z}\left(\text{XY}\right)\overline{\text{Z}}$.

Figure 4

(Color online) XRD pattern of ${\text{BiFeO}}_3$ thin film on STO(100) substrate with SRO (25 nm) bottom electrode. SRO peaks are not seen, as they are very weak and lie in the proximity of STO peaks. Inset shows (003) peak of ${\text{BiFeO}}_3$ thin film.

Figure 5

(Color online) (a) Polarized Raman spectra of $\left(001\right){\text{BiFeO}}_3$ thin film on SRO/STO in $\text{Z}\left(\text{XX}\right)\overline{\text{Z}}$ and $\text{Z}\left(\text{XY}\right)\overline{\text{Z}}$ scattering configurations at 81 K. The inset shows the magnification $50–100{\text{cm}}^{-1}$. (b) Comparison of unpolarized Raman spectra of as-grown single-domain BFO single crystal with (001)BFO thin film at 81 K.