Microstructure and enhanced electrical properties of (1−x)(Na_0.5K_0.44Li_0.06)NbO₃–x(Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)O₃ lead-free ceramics

Environment-friendly lead-free piezoelectric ceramics (1−x)(Na_0.5K_0.44Li_0.06)NbO₃–x(Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)O₃ doped with 1.0 mol% MnO₂ were synthesized by conventional solid-state sintering method. The phase transition behavior and electrical properties of the ceramics is systemically investigated. It was found that all the ceramics formed pure perovskite phase with 0.0 ≤ x ≤ 0.1, and the phase structure of the ceramics gradually transformed from orthorhombic to tetragonal phase with increasing x. Coexistence of the orthorhombic and tetragonal phase is formed in the ceramics with 0.04 ≤ x ≤ 0.06 at room temperature, and enhanced dielectric, ferroelectric and piezoelectric properties are achieved in the two phase’s region. The ceramics in the mixed phase region exhibits the following optimum electrical properties: d₃₃ = 130–147 pC/N, ε_r = 642–851, P_r = 5.51–12.44 μC/cm². The Curie temperature of the ceramics with mixed phase region was found to be 353–384 °C. The significantly enhanced dielectric properties, ferroelectric properties and piezoelectric properties with high cubic-tetragonal phase transition temperatures (T_c) make the KNLN–xBCZT ceramics showing the promising lead-free piezoelectrics for the practical applications.