Structural origin for the high piezoelectric performance of (Na0.5Bi0.5)TiO3-BaTiO3-BiAlO3 lead-free ceramics

Achieving high piezoelectric performance in the representative lead-free materials of Bi1/2Na1/2TiO3-BaTiO3 (BNT-BT) is of great interest. However, it remains a challenge in these materials, as they feature structural phases with strong octahedral tilting at morphotropic phase boundary (MPB). Herein, we obtain good piezoelectric performance with relatively large d33 value (219 pC/N), small coercive field (1.5 kV/mm), and good thermal stability in the (1-x)(Na0.5Bi0.5)TiO3-x(0.9BaTiO3-0.1BiAlO3) ternary system by crystal structure design. It is found that the incorporation of BiAlO3 with large tolerance factor can suppress the octahedral tilting and reduce the structural distortion of R3c and P4bm at MPB, and thus allows the electric field induced an extensive and reversible phase transformation. By using in-situ electric field synchrotron X-ray diffraction, it is revealed that the crystal lattice of the R3c phase with a smaller structural distortion responds more flexible to the electric field than that of the P4bm phase with a larger structural distortion. The piezoelectric strain analysis through profiles fitting indicates that the enhanced piezoelectric response attributed to both the activated domain switching and enhanced lattice strain benefited from the subtle phase structure. These findings provide further insights into the dynamic structural response of BNT-based materials, and will be helpful in designing high-performance piezoelectric materials beyond the MPB.