Thermal behavior of high-frequency optical phonons in tetragonal BaTiO3 single crystal

The temperature dependence of the optical phonon modes in the tetragonal BaTiO 3 single crystal was investigated by means of polarized Raman spectroscopy measurements. A special attention was devoted to the Raman spectra deconvolution to separate between first- and second-order bands, which can be discriminated from the difference in the temperature behavior of scattered intensity. Both A 1 mode motions along the polar c axis and E vibrations (except the well-known soft mode) normal to c were studied and discussed. The temperature dependences of frequency and damping of each optical phonon were achieved and then interpreted in terms of third- and fourth-order anharmonic potential. It was derived from this analysis that the A 1 transverse optical phonon arising from the hardening of the soft phonon of the cubic phase possesses large anharmonic motion of Ti versus O ions. A significant anharmonicity was as well found for phonons associated with O octahedral distortion.