Lanthanum induced larger polarization and dielectric relaxation in Aurivillius phase SrBi_2-x La_x Nb₂ O₉ ferroelectric ceramics

Ferroelectric ceramics SrBi_2-x La_x Nb₂ O₉ (SBLNO) were prepared by a solid state reaction process. X-ray diffraction analysis indicated that single phase layered perovskites were obtained. The maximum dielectric permittivity peak broadened gradually with the lanthanum content increasing indicated that the phase transition from normal ferroelectrics to relaxorlike ferroelectrics occurs in SBLNO. The modified Curie-Weiss (CW) law was used to describe the relaxor behavior of SBLNO ceramics. The relaxation indication coefficient (γ) was estimated from a quadratic fit of modified CW law and was found to be 1.71 and 1.72 for SBLN20 and SBLN30 specimens, respectively. The substitution of La³⁺ ions for Bi³⁺ ions in the Bi₂ O₂ layers resulted in a shift in the Curie point to lower temperature and an increase in remanent polarization and electrical field-induced strain. The maximum strain for SBLN30 specimen was found to be about 2.5× 10^-5at the 5 MV/m. The nature of relaxor behavior of SBLNO is attributed to the cationic disordering at nanoscale on A site by the La³⁺ substituted Bi³⁺ of Bi₂ O₂ layers.