Electric Field-Induced Large Strain in Ni/Sb-co Doped (Bi0.5Na0.5) TiO3-Based Lead-Free Ceramics

Lead-free piezoelectric ceramics (Bi0.5Na0.5)0.935Ba0.065Ti1−x(Ni0.5Sb0.5)xO3 (BNBT6.5-xNS) have been fabricated using conventional solid sintering technique. The effect of (Ni, Sb) doping on the phase structure and electrical properties of BNBT6.5 ceramics were systematically investigated. Results show that the addition of (Ni, Sb) destroyed the ferroelectric long-range order of BNBT6.5 and shifted the ferroelectric–relaxor transition temperature (TF–R) down to room temperature. Thus, this process induced an ergodic relaxor phase at zero field in samples with x = 0.005. Under the electric field, the ergodic relaxor phase could reversibly transform to ferroelectric phase, which promotes the strain response with peak value of 0.38% (at 80 kV/cm, corresponding to d33* = 479 pm/V) at x = 0.005. Temperature-dependent measurements of both polarization and strain confirmed that the large strain originated from a reversible field-induced ergodic relaxor to ferroelectric phase transformation. The proposed material exhibits potential for nonlinear actuators.