Forbidden raman lines in symmetrical phase

Abstract

It is well known that BaTiO₃ shows, in the cubic phase, a “forbiden” Raman spectrum₁. Recently, a careful experimental study of the light scattered from samples with various concentrations and types of impurities has shown the important role played by the defects. In this paper, we discuss a possible theoretical explanation of this unexpected spectrum in the scope of the phenomenological theory of phase transitions.