A raman and infrared spectroscopic study of the ferroelectric phase transition of (CH<SUB>3</SUB>NH<SUB>3</SUB>)<SUB>5</SUB> Bi<SUB>2</SUB> Br<SUB>11</SUB>

The Phase transition of (CH<SUB>3</SUB>NH<SUB>3</SUB>)<SUB>5</SUB> Bi<SUB>2</SUB> Br<SUB>11</SUB> from a ferroelectric to a paraelectric state has been followed by infrared and Raman spectroscopy. The libration mode of the (CH<SUB>3</SUB> NH<SUB>3</SUB>)<SUP>+</SUP> cation shows changes in the Raman spectrum probably due to order-disorder processes