Structural behaviour of the mixed-layer Aurivillius-phase Bi7Ti4NbO21

The structural behaviour of the mixed-layer Aurivillius-phase Bi7Ti4NbO21 as a function of temperature is investigated by Neutron Powder Diffraction (NPD). The first dielectric anomaly is associated to the regularisation of the "Bi4Ti3O12 part" of the structure while the "Bi3TiNbO9 part" is almost unaffected. The data recorded above the second dielectric anomaly indicate the probable existence of an intermediate orthorhombic paraelectric phase.