Angular strain-induced polarization in a ferroelectric ammonium cyclic phosphate and its wind speed sensing application

Abstract

Amino-phosphate-based ferroelectrics exhibit strong ionic conductivity, biocompatibility, high dielectric constants, and pronounced ferroelectric properties. Considering these attributes, we propose a strategy to enhance ferroelectric performance through angle strain engineering in a six-membered cyclic anionic phosphate ferroelectric, benzylammonium chlorophenyl cyclohexyl-dimethyl-phosphate (BzA·^ClPh-Cy-DMP), with the chemical formula (BzNH₃)·[O₂(cyclo-POC(^ClPh)CMe₂CH₂O)]. The compound crystallizes in the monoclinic P2₁ space group. Its non-centrosymmetric structure was confirmed by second-harmonic generation (SHG) measurements. Ferroelectricity in BzA·^ClPh-Cy-DMP was validated using a well-defined rectangular P–E hysteresis loop, yielding a saturated polarization (P_s) of 3.41 µC cm⁻² at an applied field of 9 kV cm⁻¹. Piezoresponse force microscopy (PFM) analysis visualized the presence of ferroelectric polar domains in BzA·^ClPh-Cy-DMP. The observed amplitude-bias butterfly curves and phase-bias hysteresis loops provided clear evidence of a reversible polarization switching mechanism. Furthermore, polycaprolactone (PCL) polymer composites of BzA·^ClPh-Cy-DMP enabled the fabrication of piezoelectric nanogenerators (PENGs) with advanced piezoelectric energy-harvesting performance. The top-performing 15 wt% BzA·^ClPh-Cy-DMP-PCL device achieved a peak output voltage of 23.6 V at an optimized force of 30 N. Furthermore, the device's output work efficiency (OWE) parameter, calculated at room temperature, was found to be 29.0%. Additionally, we present a novel investigation of the effect of temperature on piezoelectric energy harvesting. As temperature increases from 293 K to 315 K, the voltage increases from 23.6 V to 26.3 V and then decreases to 16.9 V at 333 K, with temperature coefficient rates of + 0.15 V K⁻¹ and −0.52 V K⁻¹, respectively. The device exhibits a rapid response time of 22.1 ms, enabling precise periodic mechanical sensing, and demonstrates its potential for wind speed estimation through a prototype piezoelectric-based wind sensor. This work offers a strategic framework for enhancing ferroelectric properties, exploring the effects of temperature on piezoelectric energy harvesting, and advancing the applications of piezoelectric materials.