Observation of ferroelectric domains in bismuth-layer-structured ferroelectrics using Raman spectroscopy

Raman spectroscopy has been used to investigate the domain structures in bismuth-layered-structured ferroelectrics (BLSFs). In Bi4Ti3O12 single crystal, the lowest frequency mode (soft mode) at ∼30 cm−1 appears exclusively for the xx polarization configuration (x∥polar axis). We found that the polarization dependence of the Raman signal exhibits spatial symmetries that reflect the presence of different domain variants present in Bi4Ti3O12. This highly anisotropic character of the soft mode shares with other BLSFs such as Bi3.25La0.75Ti3O12 and SrBi2Ta2O9, which demonstrate the usefulness of the soft-mode spectroscopy for the study of ferroelectric domain structures in BLSFs. We also applied Raman spectroscopy to in situ observation of domain structures in Bi4Ti3O12 under applied electric field.