| Summary: | Piezoelectric accelerometers using a lead-free (K,Na)NbO<sub>3</sub> (KNN) piezoceramic modified by a mixture of two Bi-based perovskites, Bi(Na,K,Li)ZrO<sub>3</sub> (BNKLZ) and BiScO<sub>3</sub> (BS), were designed, fabricated and characterized. Ring-shaped ceramics were prepared using a conventional solid-state reaction method for integration into a compression-mode accelerometer. A beneficial rhombohedral–tetragonal (R–T) phase boundary structure, especially enriched with T phase, was produced by modifying intrinsic phase transition temperatures, yielding a large piezoelectric charge coefficient <i>d</i><sub>33</sub> (310 pC/N) and a high Curie temperature <i>T</i><sub>c</sub> (331 °C). Using finite element analyses with metamodeling techniques, four optimum accelerometer designs were obtained with high magnitudes of charge sensitivity <i>S</i><sub>q</sub> and resonant frequency <i>f</i><sub>r</sub>, as evidenced by two key performance indicators having a trade-off relation. Finally, accelerometer sensor prototypes based on the proposed designs were fabricated using the KNN-BNKLZ-BS ceramic rings, which exhibited high levels of <i>S</i><sub>q</sub> (55.1 to 223.8 pC/g) and mounted <i>f</i><sub>r</sub> (14.1 to 28.4 kHz). Perfect charge-to-acceleration linearity as well as broad flat frequency ranges were achieved with excellent reliability. These outstanding sensing performances confirm the potential application of the modified-KNN ceramic in piezoelectric sensors.
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