Ordered domains in lead free 0.94(Na _0.5Bi _0.5)TiO ₃-0.06BaTiO ₃ ceramics

The microstructure of lead-free 0.94(Na _0.5Bi _0.5) TiO ₃-0.06BaTiO ₃ (BNBT-6) piezoelectric ceramics was investigated by different analysis techniques. X-ray diffraction (XRD) result reveals the coexistence of rhombohedral and tetragonal symmetry in the structure of BNBT-6 ceramics at room temperature. Selected area electron diffraction (SAED) patterns reveal the presence of ordered domains in BNBT-6 ceramics. The superlattice reflections h+1/2k+1/20 and h+1/2k+1/2l+1/2 of ordered domains mainly come from the octahedral tilt and chemical ordering of A-site atoms. High-resolution transmission electron microscopy (HRTEM) combined with image processing is an effective method to investigate the defects and the size of ordered domains in BNBT-6 ceramics. One-dimensional fringe images of superlattice reflections indicate that there are significant local Na and Bi atomic layer displacements and anti-phase boundaries as a result of chemical ordering, which provide a driving force for order-disorder transformation. A filtered HRTEM black/white image shows the size of ordered domains to be about 5-10 nm.