Microstructural Investigations and Electric Field-induced Strain of (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 Lead-Free Ferroelectric Ceramics

The field-induced giant strain of lead-free ferroelectric ceramics (1-x) (Bi0.5Na0.5)TiO3-xBaTiO(3) with x = 0 to 0.12, fabricated by an oxide mixing route, was correlated with microstructural features investigated by transmission electron microscopy. The phase investigations using x-ray diffraction reveal that the ceramics with x = 0-0.05 exhibit a rhombohedral symmetry in the perovskite structure. For x = 0.06-0.09 and x = 0.10-0.12, a transition phase with a tetragonal symmetry and a tetragonal phase were identified, respectively. Microstructural characteristics as a function of composition were compared with electrical properties. A composition range characterized by a hump around T-d in the E-T curve for the MPB can be obtained from the series of specimens, and the range is around x = 0.06 to 0.09. Within this range, the microstructure of the specimens exhibits a uniform distributed nano-domain arrangement. Moreover, coexistence of nano-domains and meso-scale domains may be observed for specimens of compositions with x = 0.3 to 0.6 and/or x = 0.9 to 0.12. It seems that the R3c and the P4bm phases appear in the materials at the same time with x from 0 to 0.12, suggesting a very similar energy level for two phases. The electrical property measurements reveal that the largest strain for specimens with x = 0.06-0.09 achieves 0.32% and is believed to be attributed to the nano-sized polarization domain switching and/or lattice softening of the phase transition of a P4bm phase.