Large electric field-induced strain and antiferroelectric behavior in (1-x)(Na_0.5Bi_0.5)TiO₃-x BaTiO₃ ceramics

The dielectric, ferroelectric, and electric field-induced strain response of (1-x)(Na_0.5Bi_0.5)TiO₃-xBaTiO₃ (NBT-BT) (0.04 ≤ x ≤ 0.10) ceramics has been systematically investigated as a function of temperature. It is found that ferroelectric and antiferroelectric (AFE)-like behavior can coexist at temperatures significantly lower than the depolarization temperature T_d (even down to as low as ambient temperature). Electron microscopy suggests that such behavior results from the electric field-dependence of fine scale octahedral tilt twinning disorder and the associated disorder in the local (ferroic) off-center displacements of the Na/Bi/Ba and Ti ions. The existence of the AFE-like behavior significantly enhances the electric field-induced strain. High bipolar strain of 0.40% and unipolar strain of 0.27% has thereby been achieved at ambient temperature in an NBT-BT, x = 0.07, ceramic. The bipolar and unipolar strains reach almost identical maximum values when the temperature is close to T_d. Giant unipolar strains of 0.42%, 0.41%, and 0.29% were observed in NBT-BT ceramics with x = 0.06, 0.07, and 0.08 at temperatures close to their T_d's of 100 °C, 50 °C, and 87 °C, respectively. This work thus provides new insight into ways to further optimize lead-free NBT-BT piezoelectric ceramics for practical use in different temperature ranges.