New (1- x)K_0.45Na_0.55Nb_0.96Sb_0.04O₃- x Bi_0.5Na_0.5HfO₃ lead-free ceramics: Phase boundary and their electrical properties

Here, we reported a high unipolar strain and large piezoelectricity in new (1-x)K_0.45Na_0.55Nb_0.96Sb_0.04O₃-xBi_0.5Na_0.5HfO₃ ceramics. The rhombohedral-tetragonal (R-T) phase boundary was constructed in the ceramics with 0.03<x≤0.05, which shows a large d₃₃ value of ∼419 pC/N. More importantly, a high unipolar strain of ∼0.31% was observed due to the multiphase coexistence. In addition, the piezoelectricity of the ceramics could be effectively enhanced if their compositions are located at the phase boundaries region, where a very low electric field of ∼1.2kV/mm can readily rotate the R/T domains. We also noticed that the deviation from phase boundary induced by applying an external electric field results in the deterioration of piezoelectricity after the "second-poling" method. We believe that as a potassium-sodium-niobate based material, the ceramics developed in this work may find practical applications in lead-free piezoelectric devices such as actuators and fuel injectors in the future owing to the significant enhancement in their piezoelectricity as well as strain.