Improved piezoelectric and energy harvesting characteristics in lead-free Fe₂O₃ modified KNN ceramics

Lead-free piezoelectric ceramics gained an increased attention due to their high piezoelectric properties combined with the absence of lead and other potentially hazardous elements. In this work, we used a unimorph cantilever beam arrangement to study piezoelectric energy harvesting in pristine K_0.5Na_0.5NbO₃ (KNN) and Fe₂O₃ modified KNN (KNFN) ceramics that are potential candidates for PZT replacement. The piezoelectric ceramics were synthesized using conventional solid state reaction method. The KNFN ceramics exhibited a superior piezoelectric performance: d₃₃ = 100 pC/N and mechanical quality factor (Q_m = 135) as compared to KNN (d₃₃ = 83 pC/N; Q_m = 76). In addition, the planar electromechanical coupling factor k_p was higher in case of KNFN having a value of 0.39 as compared to 0.34 for KNN. The KNFN harvester generated an output power of 0.38 mW/cm³ at a load resistance of 470 kΩ for a transverse displacement amplitude of 1.2 mm. The prospects of using lead-free ceramics for piezoelectric energy harvesting are discussed.