Enhancing energy-harvesting capabilities of lead-free piezoelectric materials through electrostrictive coefficient optimization

Piezoelectric energy harvesting (PEH) has emerged as a promising solution for powering low-power consumer electronic devices. Both high piezoelectric strain constants (dij) and large piezoelectric voltage constants (gij) of piezoelectric materials are crucial for PHE systems. However, raising dij is often accompanied by a notable rise in the dielectric constant, leading to a degraded gij. Here, we proposed a strategy to enhance the energy-harvesting capability by improving electrostrictive coefficients, during which the increase of dielectric response can be effectively avoided, therefore dij and gij can be improved simultaneously. By orientation optimization, B site similar ion radius element and A site small ion radius element doping, the B-site ion orderliness, lattice spacing and phase transition temperature were regulated. Then, an extremely large electrostrictive coefficient of QC11 = 0.354 m4/C2 was achieved in (K,Na)NbO3-based single crystals, surpassing Pb-based single crystals by more than five times. With this large electrostrictive performance, high values of d33 (778 pC/N) and g33 (54.6 x 10-3 Vm/ N) have been acquired. Consequently, an output power density of 12.2 mu W/mm3 at 1g acceleration was achieved in a cantilever beam PEH based on this single crystal, establishing it as one of the most prominent lead-free piezoelectric materials reported to date. This work presents a proven idea and method for enhancing the energy-harvesting capabilities of materials.