High freeze-casting cooling rates enhance the piezoelectric responses and reproducibility of porous lead zirconate titanate for sensing and energy harvesting

Porous freeze-cast ferroelectric ceramics are attractive for piezoelectric sensors and energy harvesters owing to their enhanced functional properties compared to monolithic ceramics. While the effects of the cooling rate during freeze-casting on the microstructure and mechanical properties of various oxides have been studied, this paper is the first to explore how it influences the microstructure–functional properties relationships of porous ferroelectric lead zirconate titanate. Freeze-casting cooling rates of 1–4 °C/min were investigated, and the microstructure and electromechanical properties were analyzed, informed using finite element modeling. Increasing the cooling rate from 1 to 4 °C/min reduced the effective ceramic wall thickness from 34.9 ± 8.8 μm to 14.4 ± 4.4 μm, enhanced the degree of ceramic alignment, and reduced the number of wall defects (i.e., pores within ceramic walls). These microstructural improvements led to enhanced and more consistent piezoelectric charge coefficients, d33, from 274 ± 111 pC/N at 1 °C/min to 324 ± 31 pC/N at 4 °C/min. The compressive strength of the porous PZT was also enhanced with higher cooling rates during freeze-casting, increasing from 12.3 ± 5.5 MPa to 72.1 ± 9.2 MPa. Materials fabricated using higher cooling rates exhibited greater thermal stability near the Curie point. Finite element simulations revealed that thin-walled structures led to reduced mechanical clamping and enhanced polarization under applied electric fields, thereby contributing to higher d33. These results are key optimization parameters for fabricating advanced piezoelectric composites with enhanced and reliable properties for energy harvesting, sonar, and sensing applications, while minimizing industrial waste.