Influence of ferroelectric domain walls on the Raman scattering process in lithium tantalate and niobate

Abstract

We report changes in the Raman spectra at ferroelectric domain walls in near-stoichiometric LiNbO3 and stoichiometric LiTaO3. We find a decrease of intensity for the regular bulk Raman peaks along with increases of intensity in spectral regions that correspond to phonons, which propagate at an angle with respect to the incident light. In the backscattering geometry, such modes are not supported in the bulk crystal due to momentum conservation. We confirm that these changes are due to the domain wall itself and are independent of intrinsic defects or charging effects.

Raman study of the phonon symmetries in BiFeO3single crystals

“…Moreover, we find no evidence that we are probing phonons that propagate in the x-z plane (i.e., oblique phonons 26,27 ). Indeed, such modes would exhibit LO-TO splitting as seen previously, with the presence of A(TO) and E(LO) modes leading to reduced intensities of the A(LO) and E(TO) modes.…”

“…Indeed, such modes would exhibit LO-TO splitting as seen previously, with the presence of A(TO) and E(LO) modes leading to reduced intensities of the A(LO) and E(TO) modes. 27 Hence, we observe the 13 modes expected from group theory and the modeling shows that the phonons transform according to the zone center modes' irreducible representations. Furthermore, on a polished c-axis surface we find the same number of modes as for the as-grown surface with the modes at the same frequencies (within our resolution).…”

“…At room temperature BFO has a perovskite pseudocubic unit cell (a ∼ 3.96Å) elongated along the (111) pc direction coinciding with P. The point group is C 3v , with 13 Raman active modes, of which four have A 1 symmetry (i.e., propagate along the c-axis) and nine have either E x or E y symmetry (i.e., propagate in the x-y plane), which are doubly degenerate. When the laser is not along the c-axis, phonons can propagate in the x-z plane, which could lead to LO-TO splitting (i.e., lifts the degeneracy) and hence the presence of A(TO) modes in the XX and E(LO) modes in the XY geometry, [25][26][27] which further complicates the analysis.The Raman spectra were taken in a backscattering configuration with a Horiba Jobin Yvon LabRam microscope with a 532 nm excitation source and a 10× objective (0.8 NA), 020403-1 1098-0121/2012/86(2)/020403(5) …”

Local probing of the interaction between intrinsic defects and ferroelectric domain walls in lithium niobate

“…While the first effect is due to defects, the second is due to a change in the Raman selection rules. 16 decrease in polarization for all four defect configurations. For 1NN, the defect clusters actively participate in accommodating the rapid polarization change resulting in a defect/ domain wall interaction effect.…”

“…They also spectrally overlap with the intensity changes reported due a modification of the Raman scattering selection rules by the presence of a domain wall. 16 Therefore, we do not attribute the intensity changes present at the domain wall to the presence of intrinsic defects. More importantly, we find additional changes in the Raman spectrum that correspond to frequency shifts of several modes highlighted in Figure 1 by the dotted arrows.…”