Enhanced piezoelectricity and transmittance of (1-x)K_0.5Na_0.5NbO₃-x(Ca_0.5Sr_0.5)(Zn_1/3Nb_2/3)O₃ ceramics

K_0.5Na_0.5NbO₃ is an excellent alternative to lead-based transparent ceramics because of its high Curie temperature, excellent piezoelectric properties and environmental friendliness. Normally, achieving both large piezoelectricity and high transparency seems to be difficult. Here, we developed a solid solution of (1-x)K_0.5Na_0.5NbO₃-xCa_0.5Sr_0.5Zn_1/3Nb_2/3O₃ to enhance the piezoelectric properties while maintaining a considerably high level of transparency. The x = 0.06 sample exhibits the highest transmittance of 64% and a large piezoelectric coefficient of 67 pC/N. The microstructural analysis reveals that the presence of unusually large grains (> 1 μm) in the x = 0.06 sample contributed to the enhanced piezoelectricity and transparency. These large grains decrease the density of grain boundaries, while small grains increase the relative density of the sample. Moreover, most of the grain size avoid the visible light wavelength range (400–800 nm), leading to high transparency. Our study provides new insights into the fabrication of lead-free piezoelectric ceramics that possess both large piezoelectricity and high transparency.