Large Electric Field-Induced Strain and Antiferroelectric Behavior in (1-x)(Na0.5Bi0.5)TiO3-xBaTiO3 Ceramics

The dielectric, ferroelectric, and electric field-induced strain response of (1-x)(Na0.5Bi0.5)TiO3-xBaTiO(3) (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 degrees C, 50 degrees C, and 87 degrees 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.