Broken symmetry in low-temperature BaTiO₃ phases: Strain effects probed by Raman scattering

Micro-Raman spectroscopy is utilized to study the temperature dependence of domain structures in a high-quality BaTiO₃ bulk crystal. For T=4-100 K, the spectra of the initially 90° domain wall region at room temperature exhibit the splitting of A₁ mode at ~244 cm^-1 with the appearance of an additional peak at ~263 cm^-1, the behavior of which is different from that of a sharp peak observed at ~244 cm^-1 in the single-domain region. The results imply that the strain fields exist in the domain walls at low temperatures, thus altering the local crystal symmetry.