Improved piezoelectricity in ternary potassium–sodium niobate lead-free ceramics with large strain

Abstract

Although potassium–sodium niobate (KNN)-based ceramics with good piezoelectric performance have been obtained by a phase engineering strategy, a low electric field-induced strain (<0.2%) even when applying large electric fields is observed in the ceramics prepared by normal sintering, which hardly satisfies practical application demands. Here, a ternary lead-free material system of (0.965 − x)K_0.5Na_0.5Nb_0.975Sb_0.25O₃–0.035Bi_0.5Na_0.5ZrO₃–xBiFeO₃ (KNNS–BNZ–xBF, 0 ≤ x ≤ 0.008) ceramics with excellent overall performance has been designed, aiming to achieve balanced development between piezoelectric and strain properties. A systematic study of the phase structure, electric properties and temperature stability is carried out on the ceramics, and the optimal electric properties (e.g., d₃₃ ≈ 511 pC N⁻¹, S_uni ≈ 0.202%, d₃₃* ≈ 505 pm V⁻¹, and T_c ≈ 269 °C) are obtained at x = 0.007 owing to the large tetragonality and R–T phase structure with low polarization anisotropy as well as weak energy barriers. Moreover, a new approach used to evaluate coercivity (E_c) qualitatively provides more choices to identify E_c in ferroelectrics. We believe that it may promote the application of lead-free piezoelectric materials.