Enhanced piezoelectricity from highly polarizable oriented amorphous fractions in biaxially oriented poly(vinylidene fluoride) with pure \u03b2 crystals

Yanfei Huang,Jia-Zhuang Xu,Lei Zhu,Zhong-Ming Li,Guanchun Rui,Elshad Allahyarov,Masafumi Fukuto,Qiong Li,Ruipeng Li,Gan-Ji Zhong,Philip L Taylor

doi:10.1038/s41467-020-20662-7

Abstract

Piezoelectric polymers hold great potential for various electromechanical applications, but only show low performance, with |d33 | < 30 pC/N. We prepare a highly piezoelectric polymer (d33 = −62 pC/N) based on a biaxially oriented poly(vinylidene fluoride) (BOPVDF, crystallinity = 0.52). After unidirectional poling, macroscopically aligned samples with pure β crystals are achieved, which show a high spontaneous polarization (Ps) of 140 mC/m2. Given the theoretical limit of Ps,β = 188 mC/m2 for the neat β crystal, the high Ps cannot be explained by the crystalline-amorphous two-phase model (i.e., Ps,β = 270 mC/m2). Instead, we deduce that a significant amount (at least 0.25) of an oriented amorphous fraction (OAF) must be present between these two phases. Experimental data suggest that the mobile OAF resulted in the negative and high d33 for the poled BOPVDF. The plausibility of this conclusion is supported by molecular dynamics simulations.

Highlights

Piezoelectric polymers hold great potential for various electromechanical applications, but only show low performance, with |d33 | < 30 pC/N
Despite decades of research into piezoelectric polymers, the physical mechanism for reversible polymer piezoelectricity is still a matter of debate. This debate is centered on the question: which component is primarily responsible for the observed piezoelectricity: the crystal (d333–5), the amorphous phase [d336–10 and d314,11], or the crystal-amorphous interface?12,13 Without a clear fundamental understanding of the underlying origin, it is difficult to further enhance the piezoelectric performance for polymers
All the ferroelectric domains in the crystals were aligned in the normal direction (ND) of the film

Summary

Introduction

Piezoelectric polymers hold great potential for various electromechanical applications, but only show low performance, with |d33 | < 30 pC/N. We prepare a highly piezoelectric polymer with d33 as high as −62 pC/N based on a poled biaxially oriented PVDF (BOPVDF) film containing pure β crystals. For the highly poled BOPVDF film, only the β crystal reflections were observed, as seen in Fig. 1a: (110/200)β, (310)β, (220)β, (001)β, (201)β, (311)β, and (221)β.

Results

Conclusion