New (1 − x)K0.45Na0.55Nb0.96Sb0.04O3-xBi0.5Na0.5HfO3 lead-free ceramics: Phase boundary and their electrical properties

Abstract

Here, we reported a high unipolar strain and large piezoelectricity in new (1 − x)K0.45Na0.55Nb0.96Sb0.04O3-xBi0.5Na0.5HfO3 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 ∼1.2 kV/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.