Piezoelectric and dielectric properties of 0.995K0.48Na0.48Li0.04Nb(1−x)SbxO3–0.005BiAlO3 lead-free piezoelectric ceramics

• Li, Sb, and BiAlO3 co-modified (K,Na)NbO3–based lead-free piezoelectric ceramics.
• Constructing rhombohedral- tetragonal phase boundary at around room temperature.
• An extremely small and uniform grain size resulted from the addition of BiAlO3.
• Investigating composition dependence of phase structure and electrical properties.

Lead-free 0.995 K0.48Na0.48Li0.04Nb(1−x)SbxO3–0.005BiAlO3 piezoelectric ceramics with perovskite structure were designed and prepared with conventional ceramic fabrication techniques. The phase transitions of the ceramics were determined by X-ray diffraction patterns and the temperature dependence of dielectric properties. The ceramics possessed an orthorhombic–tetragonal phase boundary with x = 0 and exhibited the coexistence of rhombohedral–orthorhombic and orthorhombic–tetragonal phase boundaries at around room temperature, with 0.02 ≤ x ≤ 0.03. Upon further increasing the Sb content, the crystal structure transformed to the rhombohedral-tetragonal phase coexistence in the composition range of 0.04 ≤ x ≤ 0.05. Next, the phase structure turned to a sole rhombohedral symmetry with x ≥ 0.06. A clearly enhanced piezoelectric activity was demonstrated for the ceramic with the rhombohedral-tetragonal phase boundary composition x = 0.05, where the values of piezoelectric constant d33, planar and thickness electromechanical coupling coefficients reached 205 pC/N, 0.360 and 0.437, respectively.

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