A high temperature stable piezoelectric strain of KNN-based ceramics

Abstract

Lead-free (1 − x)(0.96K_0.46Na_0.54Nb_0.98Ta_0.02O₃–0.04Bi_0.5(Na_0.82K_0.18)_0.5ZrO₃)–xCaZrO₃ ((1 − x)(0.96KNNT–0.04BNKZ)–xCZ) piezoelectric ceramics were prepared by the conventional solid-state reaction method. The CaZrO₃ dopant can induce a coexisting phase boundary with the transition from the orthorhombic/tetragonal phase to the R phase. Domains that exist across the grain boundary within neighboring grains appear in the ceramics with x = 0.01, which can result in an increase in ferroelectricity due to its long-range order organization. The CaZrO₃ dopant results in the formation of polar nanodomains and induces the appearance of diffuse ferroelectrics. The ceramics with x = 0.01 show optimal piezoelectric properties (d₃₃ = 300 pC N⁻¹ and = 500 pm V⁻¹ at 25 kV cm⁻¹). Meanwhile, their high level of unipolar strain reaches up to 0.175% at 35 kV cm⁻¹ at room temperature, and their field-induced strain varies less than 10% from room temperature to 120 °C. The ceramics with x = 0.02 possess a remarkably high temperature stability of (T_e = 200 °C). For x = 0.005–0.025, a higher amount of the CaZrO₃ dopant can obviously improve the temperature stability of The (1 − x)(0.96KNNT–0.04BNKZ)–xCZ system is a promising lead-free piezoelectric candidate material for commercial applications.