Excellent comprehensive electrical properties in KNN-based ceramics via synergistic effects of structural flexibility and domain engineering

Abstract

In this study, we address the limitations of KNN-based ceramics in terms of their poor comprehensive electrical properties and temperature stability, which hinder their industrial applications. To overcome these challenges, we propose a method of synergistic regulation of structural flexibility and domain engineering to achieve outstanding performance in KNN-based ceramics. Specifically, we have developed a lead-free 0.957(K_0.48Na_0.52)Nb_0.95Ta_0.06O₃–0.04(Bi_0.5Na_0.5)ZrO₃–0.003BiFeO₃ + x LiF (KNNT-BNZ-BFO/x LiF) system. At the optimal composition (x = 0.004), the ceramics exhibit a large piezoelectric coefficient (d₃₃) value of 483 pC N⁻¹ and a high Curie temperature (T_C) of 302 °C, demonstrating their superior functionality compared to previous results. The enhanced piezoelectric response can be attributed to improved structural flexibility induced by lattice softening. Furthermore, the structural flexibility should be temperature-independent, which leads to improved resistance against degradation in piezoelectric properties. Also, an abundant domain structure composed of micron-domains and nano-domains is detected in the KNNT-BNZ-BFO/0.004 LiF ceramics, which further contributes to the excellent comprehensive electrical properties. The prototype device of KNNT-BNZ-BFO/0.004 LiF buzzers is fabricated and the sound pressure level (SPL) reaches 95–98 dB at 4–5 kHz, which is comparable to that of the commercially available lead-based buzzers. This work provides a method to achieve high-performance KNN-based ceramics, which should be useful for developing lead-free piezoelectric applications.