The microstructure and dielectric relaxor behavior of BaBi_4-xLa_xTi₄O₁₅ ferroelectric ceramics

Ferroelectric ceramics BaBi_4-xLa_xTi₄O₁₅ (BBLT) were prepared with a solid-state reaction process. The obtained phases were confirmed as the Bi-layered perovskite phase with orthorhombic structure by the X-ray diffraction analysis (XRD). The dielectric relaxation was studied as a function of temperature and frequency. A dispersion of the maximum dielectric constant (ε_max) appears around the temperature of T_m, which shifts toward higher temperatures with the increase of frequency. The modified Curie-Weiss (CW) law was used to describe the relaxor behavior of BBLT ceramics. The relaxation indication coefficient (γ) was estimated with a quadratic fit of modified CW law. The coefficient firstly increases then decreases with the lanthanum increasing, which indicates that the BBT ceramics changes from relaxor-like ferroelectrics to relaxor ferroelectrics then to relaxor-like ferroelectrics with the lanthanum increasing. The relaxor nature of BBLT ceramics was attributed to the A site cationic disorder and the special relaxor behavior of BBLT ceramics was attributed to the high temperature phase transition by La³⁺ induced.