Fundamental and Second-Order Raman Spectra of BaT iO3

Polarized Raman spectra of a single-domain BaTiO3 crystal were measured over the wavenumber range 100–1600 cm −1. In addition to all the A1 and E fundamental vibrational modes reported previously, three new weak bands at 986, 1204 and 1480 cm−1 in the X(ZZ)Y geometry are observed. Based on the temperature dependence of the intensity and width of these bands, the weak bands at 986, 1204 and 1480 cm−1 are attributed to the second-order Raman spectra and the strong bands at 275 and 514 cm−1 in the A1 (TO) spectrum are confirmed to be of first order. This supports the order–disorder model of the ferroelectric phase transitions.