The structural origin of enhanced piezoelectric performance and stability in KNN-based ceramics can be attributed to the hierarchical nanodomain architecture with phase coexistence.

Because of their high toxicity, lead-based materials in electronic devices must be replaced by lead-free piezoelectric materials. However, some issues remain that hinder the industrial applications of these alternative ceramics. Here, we report the construction of a 0-3-type ceramic composite (KNNS-BNKZ: xZnO), where the Sb-doped ZnO submicronic particles were randomly distributed throughout the potassium-sodium niobate-based ceramic matrix. In this (K,Na)NbO (KNN)-based ceramic composite, superior temperature stability, excellent piezoelectric properties, and a high Curie temperature were simultaneously achieved. The unipolar strain varied from +20 to -16% when the temperature was increased from 23 to 200 °C in KNNS-BNKZ: xZnO with x = 0.75. By increasing the ZnO content from x = 0 to x = 5.0, the Curie temperature was increased from 227 to 294 °C. More importantly, the piezoelectric coefficient remained high ( d = 480-510 pC/N) for a wide range of compositions, x = 0.25-1.0. Transmission electron microscopy (TEM) experiments showed that the compensatory electric fields generated by the Sb-doped ZnO submicronic particles were responsible for the improved temperature stability. The high piezoelectricity was due to the existence of nanodomains, which were clearly observed in the TEM experiments. The results presented in this work clarify some of the physical mechanisms in this KNN-based ceramic composite, thus advancing the development of lead-free ceramics.

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(K,Na)NbO 3 (KNN)-based lead-free piezoceramics have been the spotlight in search for practically viable candidates to replace the hazardous but dominating lead-containing counterparts. In this work, BaTiO 3 (BT) modified KNN ceramics were fabricated by spark plasma sintering (SPS) and the influence of BT content as well as sintering temperature on the phase structure, microstructure, and electrical properties were investigated. It was found that the 0.96(Na 0:5 K 0:5 ÞNbO 3 -0.04BaTiO 3 (BT4) ceramics sintered at 1000 C have the optimal performance. Additionally, in-depth analysis of the electrical hysteresis revealed that the internal bias field originating from accumulation of space charges at grain boundaries is responsible for the asymmetry in the hysteresis loops.

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