Remarkably strong piezoelectricity, rhombohedral-orthorhombic-tetragonal phase coexistence and domain structure of (K,Na)(Nb,Sb)O3–(Bi,Na)ZrO3–BaZrO3 ceramics

Demands for lead-free piezoelectric ceramics increase rapidly owing to environmental concerns. Strong piezoelectricity in (K,Na)Nb-based ceramics was usually realized by taking the advantage of rhombohedral-tetragonal (R-T) phase coexistence associating with the R-T phase transition. In this paper, we report the study results on a series of dense (0.96-x)(K0.48Na0.52)(Nb0.96Sb0.04)O3−0.04(Bi0.50Na0.50)ZrO3−xBaZrO3 ceramics (abbreviated as KNNS-BNZ-xBZ ceramics), in which the one with x = 0.01 shows a giant piezoelectric coefficient d33 of 610 pC/N with quite large electromechanical coupling coefficients of kp = 0.58 and k33 = 0.69. Dielectric measurement indicated that the rhombohedral-orthorhombic (R–O) phase transition temperature TR-O, orthorhombic-tetragonal (O-T) phase transition temperature TO-T and Curie temperature TC of this ceramic are −29 °C, 43 °C and 241 °C, respectively. Meanwhile, XRD analysis unveiled that this ceramic is in rhombohedral-orthorhombic-tetragonal (R-O-T) phase coexistence at room temperature. Acid etching revealed that domain structure inside the polycrystalline grains consists of lamellar domain stacks with a large amount of hierarchical nanodomain structure existing in part of the lamellar domains. The observed strong piezoelectricity is ascribed to the R-O-T phase coexistence and the corresponding characteristic domain structure.