The phase transition behavior of ferroelectrics with perovskite structure (ABO3) has been widely studied using Raman spectropy, especially for the ceramics with nano-grains.
Take the most famous BaTiO3 (BTO) for example. The schematic structure is attached. This kind of perovskite undergoes different crystal structures when the temperature decreases from above the Curie temperature (120C): Pm3m (cubic T>120C) --> P4mm (tetragonal, 5C
I remember that in 2012 in Bangalore at the last ICORS (Raman) conference S. Krylova had a talk about an anomalous dependences of parameters of internal
vibrations modes in perovsite-like crystals. It may help.
The various modifications of BT have a different number of Raman modes because they have a different symmetry. The number and type of Raman active modes can be calculated from symmetry considerations. However a precise assignment of the Raman modes to the observed bands can only be performed in single crystals changing the polarization of incident beam and orientation of crystal. In the case of ceramics and particles the assignment of Raman modes and the interpretation of the spectrum is more difficult owing to the random orientation of the crystallites and broadening effects. Moreover, BT spectra show some peculiarities such as the persistance of some modes above the Curie temperature related to the existence of polar clusters.There are several good papers on the Raman scattering of BT and you can have some useful suggestions if you get in touch with Marco Deluca (University of Leoben, Austria), [email protected], or Jan Petzet (Institure of Physics, Academy of Science of the Czech republic, Prague), [email protected]. They are experts of the field.
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