Structural evolution, dielectric and ferroelectric properties of (1-x)Bi_0.5Na_0.5TiO₃-xBa_0.3Sr_0.7TiO₃ ceramics

(1 − x)Bi_0.5Na_0.5TiO₃−xBa_0.3Sr_0.7TiO₃ (abbreviated as BNT-BST, x = 0.05 ~ 0.40) was prepared by a conventional ceramic processing method and their structural evolution, dielectric and ferroelectric properties were investigated. The structure of the BNT-BST ceramics changes from phase coexistences of Rhombohedral-Tetragonal (x ≤ 0.10) to Tetragonal-Cubic (x ≥ 0.35), across a dominant Tetragonal phase region (0.15 ≤ x ≤ 0.30). By increasing BST content, the grain size of the BNT-BST ceramics slightly decreases, while the temperature T_m of the maximum dielectric constant gradually goes downward from ~ 250 °C to near room temperature. Meanwhile, with the increase of measuring frequency, the T_m increases for the BNT-BST ceramics with x ≥ 0.15, indicating their relaxor ferroelectric characteristics. Room temperature P-E loop test results show that both coercive field E_c and remnant polarization P_r gradually reduce with the increase of x value for relaxor BNT-BST ceramics. Both high peak dielectric constant (ε_r > 6000 at T_m) and saturated polarization (P_s ~ 30 µC/cm²), as well as tunable remnant polarization P_r are obtained in relaxor BNT-BST ceramics suitable for capacitor candidate materials.