Tailoring micro-structure of eco-friendly temperature-insensitive transparent ceramics achieving superior piezoelectricity

Transparent ferroelectrics with high piezoelectricity are highly desirable for acousto-optic-electrical multifunctional coupling devices. However, it is challenging to simultaneously achieve high piezoelectricity and perfect transparency in lead-free piezoelectric ceramics because of the contradiction between the inherent characteristics of traditional high piezoelectricity and the transparency. Here, we demonstrate an efficient method to tailoring the microstructure in originally poor piezoelectricity fine-grain KNN-BNN ceramics to simultaneously exhibit excellent transparency, an superior piezoelectric coefficient (∼185 pC/N, highest in KNN-based transparent ceramics), an excellent EO coefficient (∼84 pm/V), and high T_c (∼350 °C). Combining the multiple in-situ characterizations and DFT simulations, we found that both the piezoelectricity and EO effect of fine-grain KNN transparent ceramics can be greatly improved without greatly reducing the transparency via tailoring the structure of phase and domains to enhance local inhomogeneity, enabling prominent acousto-optic-electrical multifunctional coupling in vivid potential applications, such as self-energy-harvesting touch screens, invisible robotic devices and electro-optic (EO) devices.