Ultrahigh energy harvesting properties in temperature-insensitive eco-friendly high-performance KNN-based textured ceramics

Mechanical energy-driven wireless charging technology has recently gained increasing attention. In this work, high-performance potassium sodium niobate (KNN)-based textured ceramics and their potential application in energy harvesting devices are systematically investigated. A series of lead-free 0.99K 0.5 Na 0.5 Nb (1− x ) Ta x O 3 -0.01Bi(Ni 2/3 Nb 1/3 )O 3 [KNNTa-BNN] piezoceramics were designed and prepared to search for good comprehensive properties. The comprehensive performance of KNN-based piezoelectric ceramics has reached a new level in T-Ta-9 ( d 33 ∼ 435 pC N −1 , k p ∼ 71%, T c ∼ 360 °C) via the synergy of the textured structure ( f (00 l ) > 94%) and multiphase coexistence (O-T) near room temperature. Based on the advanced in situ TEM and PFM analyses, it was found that the regular large-scale domains and corresponding poling patterns of the T-Ta-9 can be well maintained at relatively high temperatures (180-330 °C), resulting in excellent temperature stability. Hence, the d 33 value of T-Ta-9 can be maintained above 300 pC N −1 over a wide range from room temperature to 300 °C, which rarely happens in the previously reported KNN-based materials. More importantly, the piezoelectric circular diaphragm (PCD) vibration energy harvester based on the T-Ta-9 texture ceramic possesses high output voltage ( U ∼ 13 V) and output power ( W ∼ 3 mW), and can still maintain above 60% after being heated at 200 °C for 30 min. This work represents a significant advancement in the lead-free piezoelectric energy-harvesting field (especially for high-temperature applications) and can provide guidelines for future efforts in this direction. Through the simultaneous use of composite design and template grain growth technology, the comprehensive performance of KNN-based piezoelectric ceramics has been significantly improved via the synergy of the textured structure and multiphase coexistence.