Dielectric and Ferroelectric Properties in Highly Substituted Bi2Sr(A)TiNb2O12 (A = Ca2+, Sr2+, Ba2+) Aurivillius Phases

Structure property relationships were determined for the family of three-layer Aurivillius materials Bi2Sr(A)TiNb2O12 (A = Ca2+, Sr2+, Ba2+). X-ray and neutron diffraction along with selected area electron diffraction indicate that Bi2SrBaTiNb2O12 crystallizes in the nonpolar I4/mmm space group, whereas the polar B2cb space group best describes Bi2SrCaTiNb2O12 and Bi2Sr2TiNb2O12 Despite the different space groups, all three compositions show relaxor behavior as evidenced through P(E) and dielectric measurements. These relaxor properties are derived from the extensive amount of disorder in each composition that is found at every cationic crystallographic site and do not depend on the space group. This disorder is so extensive that it disrupts the ferroelectric properties allowed by symmetry in the B2cb space group. This work demonstrates the important role of cation substitution and site disorder in these three-layered Aurivillius materials and its significant effect on both ferroelectric and dielectric properties.