Fig. 2: Fabrication and characterization of lead-free SP-1-3 piezo-elements.

a Schematic diagram of the fabrication process of SP-1-3 piezo-elements. The left insets show SEM images of the KNNS95 precursor (top) and a mixture of KNNS95 precursor and polystyrene (bottom).Scale bars are 10 μm (top) and 50 μm (bottom). b Rietveld refinement of macroscopic structure of dense KNNS95 ceramics. The inset shows expanded part at the 2Theta range of 45°−46°. c Room temperature XRD patterns of piezo-composites with different diameters of PS measured at the 2Theta range of 45°−46°. d, e Amplitude (d) and SS-PFM curves (e) of dense KNNS95 ceramics. Scale bar is 1 μm. f Local SEM of SP-1-3 composite, showing the dense, porous, and epoxy resin portion in the composite. Scale bar is 500 μm. g SEM image of SP-1-3 composite and corresponding element mapping. Scale bar is 200 μm. Experiments in f, g were repeated three times with similar results. h, i Bipolar strain curves (h) and d₃₃-E loops (i) of dense KNNS95 ceramics (D-C), sandwich ceramics (S-C), and SP-1-3 composites. j Variation tendency of d₃₃ and ε_r of D-C, S-C, and SP-1-3 composites. k Comparison of g₃₃ and d₃₃ × g₃₃ values between lead-free piezo-materials in this work and lead-based counterparts in other works⁵⁵. Source data are provided as a Source Data file.