Large electric-field-induced strain in Zr-modified lead-free Bi0.5(Na0.78K0.22)0.5TiO3 piezoelectric ceramics

Lead-free Zr-modified Bi0.5(Na0.78K0.22)0.5TiO3 ceramics (BNKTZ-100x, with x = 0–0.05) were synthesized by a conventional ceramic fabrication process and its influence on crystal structure and electromechanical properties was investigated. The temperature-dependent dielectric peaks of the BNKTZ-100x   ceramics broadened and ferroelectric polarizations decreased with increasing Zr concentration. The BNKTZ-3 ceramics showed an enhanced unipolar field-induced strain of 0.43%. The dynamic piezoelectric coefficient (d33* = Smax/Emax) obtained for this composition was 614 pm/V, much higher than that of polycrystalline lead-free and hard Pb(Zr,Ti)O3 ceramics. These results indicate that an appropriate amount of Zr substitution significantly enhances the field-induced strain level of BNKT ceramics and can be considered as one of promising candidate materials for lead-free electromechanical actuator applications.