Lead-free piezoelectric ceramics based on (0.97 - X)K_0.48Na _0.52NbO₃-0.03Bi_0.5(Na_0.7K _0.2Li_0.1)_0.5ZrO₃-xB _0.5Na_0.5TiO₃ ternary system

In this work, the ternary system of potassium-sodium niobate has been designed to enhance the piezoelectric properties without sacrificing the Curie temperature greatly, and (0.97 - x)K_0.48Na_0.52NbO ₃-0.03Bi_0.5(Na_0.7K_0.2Li _0.1)_0.5ZrO₃-xB_0.5Na _0.5TiO₃ ceramics have been prepared by the conventional solid-state method. The effect of B_0.5Na_0.5TiO₃ content on the microstructure and electrical properties of the ceramics is studied. The phase diagram shows a phase boundary of the rhombohedral-tetragonal (R-T) phase coexistence in the composition range of 0.5% < x < 1.5%, and then an enhanced dielectric, ferroelectric, and piezoelectric behavior is obtained at such a phase boundary zone. The ceramic with x = 0.01 has an optimum electrical behavior of d₃₃ ∼ 285 pC/N, k_p ∼ 0.40, ε_r ∼ 1235, tan δ ∼ 0.031, P_r ∼ 14.9 μC/cm², and E_c ∼ 15.2 kV/cm, together with a high Curie temperature of ∼347 °C. The large d₃₃ in such a ternary system is due to a composition-induced R-T phase transition and a higher ε_rP_r, and the thermal stability performance is strongly dependent on the phase structure. As a result, the design of the ternary system is an effective way to enhance the piezoelectric properties of potassium-sodium niobate materials.