Structural and dielectric properties of La and Nb co-substituted Bi0.5(Na0.84K0.16)0.5TiO3-SrTiO3 ceramics

In this article La and Nb co-substitution effect on the crystal structure, microstructure, ferroelectric and dielectric properties of 0.96[{Bi_0.5 (Na_0.84 K_0.16)_0.5}_1-xLa_x(Ti_1-y Nb_y)O₃]-0.04SrTiO₃ (BNKLTN-ST, where (x=y) = 0.00 - 0.020) ceramics has been investigated. The ceramics with x,y ≤ 0.010 have pure perovskite structure, while a secondary phase appears in the sample with x=y = 0.020. X-ray diffraction patterns revealed that La and Nb co-doping resulted in a transition from coexistent rhombohedral and tetragonal phases to pseudocubic symmetry. The co-doping of La and Nb slightly increased the average grain size. The maximum permittivity temperature (T_m) increased with increasing La and Nb contents, but the values of depolarization temperature (T_d) as well as maximum dielectric constant (ε_m) decrease gradually. La and Nb addition interrupted the polarization and reveals that the ferroelectric (FE) order of unmodified BNKT-ST ceramics lead to a declination of remnant polarization along with coercive field. The results shows that La and Nb co-doping into BNKT-ST ceramics induces a phase transition from relaxor FE to ergodic relaxor phase with a substantial deterioration of the long-range FE order.