Forbidden raman lines in symmetrical phase

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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.