Theoretical and experimental study of Raman spectra of pre-perovskite PbTiO3

The assignment of microscopic Raman spectra on powdered samples of pre-perovskite PbTiO3 (space group I4/m) has been established according to the correspondence between the experimental and theoretical frequency and relative intensity data. We find no giant longitudinal-optical (LO) and transverse-optical (TO) splittings in pre-perovskite PbTiO3. In contrast to conventional perovskite, the largest pre-perovskite LO-TO splitting comes from its stiffest A(u) mode instead of from its softest mode. The pre-perovskite's Born effective charges, dielectric tensors, and infrared frequencies are also calculated to determine its lattice dynamics and optical properties, and compared with the conventional perovskite PbTiO3. The results provide invaluable information for use in further research on PbTiO3 phase transition. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3632070]