Textured Lead-Free Piezoelectric Ceramics for Flexible Energy Harvesters.

A lead-free (K,Na)NbO 3 -based piezoelectric ceramic is textured along the (001) direction using the NaNbO 3 (NN) seeds. The composition 0.96(K 0.5 Na 0.5 )(Nb 0.965 Sb 0.035 )O 3 -0.01CaZrO 3 -0.03(Bi 0.5 K 0.5 )HfO 3 (KNN) is found to provide an excellent combination of electromechanical coefficients at room temperature. The textured composition with 5 wt % NN template (KNN-5NN) exhibits considerably improved electromechanical coefficients, d 33 ∼ 590 pC/N, k 31 ∼ 0.46, and d 31 ∼ 215 ×10 -12 C/N, at room temperature. A flexible piezoelectric energy harvester (F-PEH) is fabricated using the textured KNN-5NN ceramic and tested under cyclic force. F-PEH exhibits enhanced output voltage ( V oc ∼ 25 V), current ( I ∼ 0.4 μA), and power density ( P D ∼ 5.5 mW/m 2 ) ( R L of 10 MΩ) in the off-resonance frequency regime. In comparison to the random ceramic KNN-0NN-based F-PEH ( V oc ∼ 8 V and I ∼ 0.1 μA), the textured F-PEH significantly outperformed energy harvesting capability due to the large figure-of-merit value ( d 31 × g 31 ) ∼ 3354 ×10 -15 m 3 /J. This work provides a methodology for texturing lead-free materials and further implementing them in flexible energy harvesting devices and sensors.