Textured Lead-Free Piezoelectric Ceramics for Flexible Energy Harvesters.

A lead-free (K,Na)NbO3-based piezoelectric ceramic is textured along the (001) direction using the NaNbO3 (NN) seeds. The composition 0.96(K0.5Na0.5)(Nb0.965Sb0.035)O3-0.01CaZrO3-0.03(Bi0.5K0.5)HfO3 (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, d33 ∼ 590 pC/N, k31 ∼ 0.46, and d31 ∼ 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 (Voc ∼ 25 V), current (I ∼ 0.4 µA), and power density (PD ∼ 5.5 mW/m2) (RL of 10 MΩ) in the off-resonance frequency regime. In comparison to the random ceramic KNN-0NN-based F-PEH (Voc ∼ 8 V and I ∼ 0.1 µA), the textured F-PEH significantly outperformed energy harvesting capability due to the large figure-of-merit value (d31 × g31) ∼ 3354 ×10-15 m3/J. This work provides a methodology for texturing lead-free materials and further implementing them in flexible energy harvesting devices and sensors.