Superior piezoelectricity and rhombohedral-orthorhombic-tetragonal phase coexistence of (1 − x)(K,Na)(Nb,Sb)O3−x(Bi,Na)HfO3 ceramics

Requirements for lead-free piezoelectric ceramics are growing increasingly strong owing to environmental concerns. This paper reports the study results of (1 − x)(K0.48Na0.52)(Nb0.96Sb0.04)O3–x(Bi0.50Na0.50)HfO3 ceramics. It was found that all the ceramics with 0.035 ≤ x ≤ 0.047 show rhombohedral−orthorhombic−tetragonal (R−O−T) phase coexistence at room temperature and the one with x = 0.045 has a giant piezoelectric coefficient d33 of 540 pC/N. Unexpectedly, the rhombohedral−orthorhombic phase transition temperature is almost independent of the (Bi0.50Na0.50)HfO3 content. Moreover, electromechanical coupling factor kp is temperature-stable in orthorhombic phase. The results demonstrate that superior piezoelectricity can be obtained in a (K,Na)NbO3-based ceramic of R−O−T phase coexistence.