Thermal behavior of high-frequency optical phonons in tetragonal BaTiO sub(3) single crystal

The temperature dependence of the optical phonon modes in the tetragonal BaTiO sub(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 sub(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 sub(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.