Anharmonicity and local noncentrosymmetric regions in BaTiO3 pressed powder studied by the Raman line temperature dependence

The temperature dependencies of position, width, and integral amplitude the E(TO) line near 307 cm(-1) in Raman spectra in barium titanate powders with different non-hydrostatic pressure and temperature treatment were studied. It was found that parameters of the E(TO) line near 307 cm(-1) are different in the crystal, the untreated powder, the powder treated by the non-hydrostatic pressure, and the powder annealed after the pressure treatment. The line width (FWHM) increase with temperature according to Klemens model. It indicates that the origin of the line broadening is the anharmonicity of the E(TO) phonons. The pressure treatment changes the anharmonicity of the phonon potential. It was found that the temperature dependence of the integral intensity of the E(TO) line is similar to that of the second optical harmonic signal and reflects the presence of the local polar regions. Thus, the E(TO) line in the Raman spectrum allows one to characterize the average polarity of local regions and their anharmonicity depending on non-hydrostatic pressures and thermal treatment.