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 Bi 2 Sr(A)TiNb 2 O 12 (A = Ca 2+, Sr 2+, Ba 2+ ). X-ray and neutron diffraction along with selected area electron diffraction indicate that Bi 2 SrBaTiNb 2 O 12 crystallizes in the nonpolar I 4/ mmm space group, whereas the polar B 2 cb space group best describes Bi 2 SrCaTiNb 2 O 12 and Bi 2 Sr 2 TiNb 2 O 12 . 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 B 2 cb 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.