Improvement of (K,Na)NbO3-based lead-free piezoelectric ceramics by asymmetric octahedra

Abstract

Due to their excellent piezoelectric properties, including a coupling factor k_p = 0.55, dielectric constant ε^T₃₃/ε₀ = 2725, piezoelectric constant d₃₃ = 375 pC N⁻¹, Q_m = 60, and dielectric tan δ = 1.87%, 0.891(K_0.37Na_0.63)_0.86Ca_0.04Li_0.02Nb_0.85O_3−δ–0.041K_0.85Ti_0.85Nb_1.15O₅–0.055BaZrO₃–0.0016Co₃O₄–0.0025Fe₂O₃–0.0069ZnO ceramic without Ta, Sb, Bi, or Hf is promising as a lead-free piezoelectric ceramic. In this system, a solid solution of BaZrO₃ into (K_0.37Na_0.63)_0.86Ca_0.04Li_0.02Nb_0.85O_3−δ effectively contributes to both the piezoelectric properties and the stability around room temperature. The solid solution of BaZrO₃ induces asymmetry in the BO₆ octahedra in the c-axis direction, improving k_p, steeply increasing ε^T₃₃/ε₀ at room temperature, while reducing the temperature dependence of ε^T₃₃/ε₀.