Enhanced electric-field-induced strain at the ferroelectric-electrostrcitive phase boundary of yttrium-doped Bi0.5(Na0.82K0.18)0.5TiO3 lead-free piezoelectric ceramics

The effects of Y doping on the crystal structure, and on the ferroelectric and the piezoelectric properties of Bi0.5(Na0.82K0.18)0.5TiO3 ceramics have been investigated. The Y doping induced a transition from a ferroelectric (FE) tetragonal to an electrostrcitive (ES) pseudocubic phase, leading to the degradations of the dielectric constant, loss tangent, the remnant polarization, coercive field, and piezoelectric coefficient d33. However, the electric-field-induced strain was significantly enhanced by the Y-doping-induced phase transition and reached the highest value of Smax / Emax = 278 pm/V when 0.7 wt% Y2O3 was doped. The abnormal enhancement in strain was attributed to the coexistence of FE and ES phases, which provided more degrees of freedom for domain reorientation under electric fields.