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

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 0.48 Na 0.52 )Nb 0.95 Ta 0.06 O 3 –0.04(Bi 0.5 Na 0.5 )ZrO 3 –0.003BiFeO 3 + x LiF (KNNT-BNZ-BFO/ x LiF) system. At the optimal composition ( x = 0.004), the ceramics exhibit a large piezoelectric coefficient ( d 33 ) 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.