Raman studies of underdamped soft modes in PbTiO3

Unlike other ferroelectric perovskites, PbTiO3 displays temperature-dependent Raman spectra consisting of underdamped modes, including the "soft" transverse-optical (TO) modes. Moreover, the softest TO mode shows linewidth divergence at the ferroelectric-to-paraelectric transition. Also in contrast to previously studied perovskites, Raman selection rules are rigorously obeyed in both the ferroelectric and paraelectric states. © 1970 The American Physical Society.