Tailoring micro-structure of lead-free KNN piezoelectric ceramics for force-sensitivity smart window

Ferro/piezoelectric transparent materials with both excellent piezoelectricity and transparency are of great interest for irreplaceable applications in numerous fields such as photoacoustic imaging, and transparent robots. Nevertheless, developing a lead-free ferroelectric ceramic that meets both distinct transparency and high piezoelectricity has always been challenging. Herein, the simple single Sm³⁺ doped KNN ferroelectric ceramics (xSm) are designed to improve the transparency and achieve reasonable piezoelectricity. The results indicate that although the donor doping effect of Sm³⁺ significantly improves the transparency by mainly causing grain refinement and densification improvement, it also enhances the relaxor behavior of KNN ceramics and weakens the piezoelectricity. Despite this, with proper Sm doping, reasonable piezoelectricity can still be achieved in the xSm transparent ceramics without causing a significant decrease in Curie temperature. Ultimately, excellent comprehensive performance was achieved in the 1.0Sm ceramic (T ~ 65% at 900 nm, TC ~ 395 ℃, d33 ~ 65 pC/N), competitively in the KNN-based transparent ceramics. In force sensitivity testing, the 1.0Sm ceramic also exhibits prominent force response electrical output characteristics, which is expected to be applied in smart windows that require real-time pressure detection. This work furnishes a methodology for the fabrication of KNN-based transparent piezoceramics, while contemporaneously recommending innovative perspectives for broadening their range of applications.