Raman study of the improper ferroelectric phase transition in iron iodine boracite

The reduction in the dielectric anomaly near Tc in improper ferroelectrics suggests that this behavior may be exploited to significantly enhance the figure-of-merit for pyroelectric infrared detection. This "reduction" is associated with a decoupling of the thermal and dielectric responses which, in turn, reflects the unusual nature of the lattice instability at the phase transition. In order to elucidate the characteristics of the phonon behavior connected with the lattice instability, Raman scattering of Fe 3 B 7 O 13 I has been examined in both the paraelectric and ferroelectric phases. The results of this study as well as results from earlier measurements on other boracites, provides insight into the nature of the mode softening.