Large strain in lead-free piezoelectric (1−x−y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBi0.5Li0.5TiO3 system near MPB prepared via the combustion technique

Lead-free ferroelectric ceramics in the (1−x−y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBi0.5Li0.5TiO3 (1−x−yBNT–xBKT–yBLT) ternary system with 0.18≤x≤0.26 and 0≤y≤0.12 were prepared by the combustion technique. The effects of x and y contents on the crystal structures and electrical properties were examined. The results indicated that a coexistence of rhombohedral (R) and tetragonal (T) phases occurs in the system, which tends to evolve into tetragonal symmetry when the x and y contents are increased. The diffuseness exponent (γ) of the ceramics was between 1.6 and 1.9, indicating that the (1−x−y)BNT–xBKT–yBLT solid solutions exhibited diffuse phase transition behavior. The change in P–E loops indicated that the long-range ferroelectric order of the sample was affected and transitioned to the polar nano-region with increase of x and y contents. The polarization hysteresis loop transitioned from well saturated loops a typical of a normal ferroelectric to a pinched loop and finally to a relaxor state with the increase of x and y contents. The coexistence of polar and non-polar phases at the MPB (0.77BNT–0.20BKT–0.03BLT) likely caused the pinching behavior with large strains of approximately ~0.36% (measured at 5 kV/mm) and Smax/Emax values of ~727 pm/V which are suitable for actuator applications.