Raman study of low temperature phase transitions in bismuth titanate, Bi<SUB>4</SUB>Ti<SUB>3</SUB>O<SUB>12</SUB>

An anomalous line narrowing along with the appearance of several new lines on cooling Bi4Ti3O12 ceramics, indicates a subtle phase transition in the 150-200 K region. In the same temperature range, anomalies in dielectric properties (dielectric constant, coercive field, and spontaneous polarization) of single-crystal Bi4Ti3O12 were reported. A possible subtle monoclinic-orthorhombic phase change, combined with a continuous ordering of dipoles associated with Bi3+ lone pair electrons and TiO6 octahedra, may be responsible for these results