Ferroelectric distortion in Bi{sub}4Ti{sub}3O{sub}12 studied by neutron powder diffraction

摘要

Crystal structures of Bi{sub}4Ti{sub}3O{sub}12 ferroelectrics have been investigated by high-temperature neutron powder diffraction study. The ferroelectricity in Bi{sub}4Ti{sub}3O{sub}12 is shown to originate from the in-plane displacement of TiO{sub}6 octahedra with respect to heavy Bi ions, and that the off-center Ti displacement in the octahedra plays a minor role. Bond valence analysis shows that the underbonding of Bi with the adjacent oxide ions at the perovskite A site in high-temperature paraelectric state plays an essential role in the ferroelectric phase transition in the Bi{sub}4Ti{sub}3O{sub}12 system.