RAMAN-STUDY OF LOW-TEMPERATURE PHASE-TRANSITIONS IN BISMUTH TITANATE,BI4TI3O12

An anomalous line narrowing along with the appearance of several new l ines on cooling Bi4Ti3O12 ceramics, indicates a subtle phase transitio n in the 150-200 K region. In the same temperature range, anomalies in dielectric properties (dielectric constant, coercive field, and spont aneous polarization) of single-crystal Bi4Ti3O12 were reported. A poss ible subtle monoclinic-orthorhombic phase change, combined with a cont inuous ordering of dipoles associated with Bi3+ lone pair electrons an d TiO6 octahedra, may be responsible for these results.