Phase structure, microstructure and piezoelectric properties of perovskite (K0.5Na0.5)0.95Li0.05NbO3–Bi0.5(K0.15Na0.85)0.5TiO3 lead-free ceramics

Lead-free ceramics (1 − x)(K0.5Na0.5)0.95Li0.05NbO3–xBi0.5(K0.15Na0.85)0.5TiO3 [(1 − x)KNLN–xBKNT] with x = 0–0.04 were successfully synthesized by conventional solid-state sintering. Effects of Bi0.5(K0.15Na0.85)0.5TiO3 (BKNT) on the phase structure, microstructure and electrical properties of the (1 − x)KNLN–xBKNT ceramics were investigated. BKNT strongly affected the sintering behavior, densification and microstructure of the ceramics. X-ray diffraction analysis revealed that all the (1 − x)KNLN–xBKNT ceramics possessed pure perovskite structure, showing symmetries of orthorhombic at x < 0.005, and tetragonal at x ≥ 0.015 at room temperature. Coexistence of orthorhombic and tetragonal phases was identified in the range of 0.005 ≤ x < 0.015. The 0.99KNLN–0.01BKNT ceramics showed the optimum piezoelectric, ferroelectric properties and high Curie temperature, which were as follows: d33 = 240 pC/N, kp = 0.455, Pr = 20 μC/cm2, Ec = 20.8 kV/cm and Tc = 469 °C. The mechanism of the enhanced piezoelectric properties was also discussed. These results indicate that this system looks a promising candidate for lead-free piezoelectric materials.