Pressure dependence of the Raman active modes in Bi sub 4 Ti sub 3 O sub 12.

Bismouth titanate (Bi sub 4 Ti sub 3 O sub 12), a layer-type ferroelectric material crystallizing in the monoclinic system, has been investigated by high-pressure Raman technique up to 17 GPa in a diamond anvil cell. A pressure-induced phase transition occurs near 3 GPa, and the softening of the lowest Raman mode near 31 cm sup -1 seems to be associated with this transition. Furthermore, the Raman data as well as absorption measurements indicate that a second phase transition occurs near 11 GPa. This transition may be due to a change from the ferroelectric to the paraelectric phase under the influence of pressure.