Microstructure and electrical properties of (1 − x)K_0.5Na_0.5NbO₃–x(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ lead-free piezoelectric ceramics

The (1 − x)K_0.5Na_0.5NbO₃ − x(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (KNN–BCTZ) lead-free ceramics were fabricated by conventional solid-state sintering technique. The microstructure and electrical properties of the ceramics were investigated. The X-ray diffraction analysis revealed that the ceramics formed a single phase perovskite solid solutions with the symmetry of orthorhombic at x < 0.03. The crystal phase of the ceramics changed from orthorhombic phase to pseudocubic phase when x > 0.04. The coexistence of orthorhombic and pseudocubic (tetragonal) phases was observed near room temperature when 0.03 ≤ x ≤ 0.04. The grains grew up obviously when 2 mol% BCTZ was added, but the grain size was found to reduce gradually with further increasing BCTZ content. The T _C and T _O-T decreased with the increasing BCTZ content. The ferroelectric and piezoelectric properties were abruptly degraded as x ≥ 0.05. Optimum properties (d ₃₃ = 136 pC/N, k _p = 27 %, k _t = 26.5 %, Q _m = 25, P _r = 14.67 μC/cm², E _c = 11.23 kV/cm, T _C = 347 °C, \(\varepsilon_{33}^{\text{T}} /\varepsilon_{0} = 8 6 1. 5\), tan δ = 0.04) were obtained for the ceramica with x = 0.03.