No abstract

The temperature dependence of both Stokes and anti‐Stokes Raman spectra in a BaTiO3 single crystal was studied. Based on the theory of the Raman scattering cross‐section for one‐ and two‐phonon scattering, the strong bands at 275 and 514 cm−1 in theX(ZZ)Y geometry are confirmed to be of first order. This supports the order–disorder model of the ferroelectric phase transition.

Polarized Raman spectra of LBO single crystal were recorded in the temperature range 300-870 K. At room temperature, 26A,, 27A,, 26B, and 26B2 modes expected from group theoretical analysis are observed by various scattering geometries. Among them, the internal bands are tentatively assigned to vibrations of the BO, triangle and BO, tetrahedron in terms of factor group analysis. Based on the temperature dependence of the wavenumbers, the Griineisen parameters of A,(TO), &(TO) and &(TO) modes are calculated and discussed. No soft modes are observed in the above temperature range, implying that no displacive-type phase transition takes place there. The crystal structure of LBO below 870 K is stable. 105 optical vibration modes, 26A1 + 27A, + 26B, Modes A,, B , and B, are also infrared active, their polarizations being parallel to the c, a and b axes of the crystal, respectively.