Energy-storage study in lead-free anti-ferroelectric Bi_0.5Na_0.5Tio₃-BaTiO₃-K_0.5Na_0.5NbO₃ ceramics

Lead-free (1-x-y)Bi_0.5Na_0.5TiO₃-xBaTiO₃-yK_0.5Na_0.5NbO₃ (BNT-BT-KNN) ceramics were fabricated by traditional sintering method. The X-ray diffraction patterns showed that the ceramics are all crystallized into a perovskite structure phase. Measurements of temperature-dependent dielectric constants showed the two typical shoulders observed in the BNT-BT binary system, indicating that the ceramics are also of relaxor anti-ferroelectric nature. Moreover, it was observed that the dielectric constants decreased sharply with the increase of KNN addition, while maintained the same level when the BNT/BT ratio changed. The P-E hysteresis loops showed that the saturated polarization and the remnant polarization both decreased with the increasing addition of KNN, while the reduction of the BNT/BT ratio enhancesd the saturated polarization. The energy-storage density calculated from the P-E loops also increased with the decrease of KNN addition and BNT/BT ratio, which further demonstrated that the key for improving the energy density of BNT-BT-KNN ceramics is relatively low addition of KNN and low BNT/BT ratio.