Recently, a precession X-ray study has discovered that ferroelectric BaTiO₃ single crystals have a coherent hybrid structure (CHS) that consists of tetragonal and monoclinic lattices that share the (101) face of the tetragonal [1,2]. Microscopic observations attest that the single crystal has two kinds of stripes (grey and yellow regions). Raman spectra were measured at room temperature in a backscattering geometry on a 4x4x4 mm³ single crystal, with the sample placed under the microscope with ×10, ×40 and ×100 magnifications. The difference of the relative intensities between the different magnifications at the 90° domain indicates that the stripes consist of several elongated domains, which are consistent with the CHS. Two kinds of domains have been observed by the Raman measurements, which are identified as light and dark spots under the optical microscope. Raman spectra of all sides of the cubic crystal have been collected at several scattering configurations. The spectra structures and line-widths are strongly affected when the laser direction is parallel to the b-axes and the polarization parallel to the a- or c-axes of the 90^ο domain (ac-side). It appears that there is a symmetry reduction, which affects the polarization selection rules of the Raman active phonons. The results are in agreement with the coexistence of the two (tetragonal and monoclinic) lattices.

References

   [1] Y. Yoshimura, A. Kojima, N. Tokunaga, K. Tozaki, T. Koganezawa, Phys. Lett. A 353, 250 (2006).

   [2] Y. Yoshimura, M. Morioka, A. Kojima, N. Tokunaga, T. Koganezawa, K. Tozaki, Phsy. Lett. A 367, 394 (2007).

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