AFM Materials Journal Club

Ferroelectric Fibers with Internal-Strain-Induced Self-Poling for Poling-Free Flexible Nanogenerators

by Ruijian Zhu, Zengmei Wang, He Ma, Guoliang Yuan, Fengxia Wang, Zhenxiang Cheng, Hideo Kimur

Nano Energy, 2018, 50, 97

Self-poling is a phenomenon of macroscopic polarization in as-grown ferroelectrics without the need of external electrical stimuli. Self-poled ferroelectric materials have many applications advantages, e.g., simplified, novel devices free from electrodes and external poling. Most of these materials are 2D epitaxial films. The authors report a unique and effective approach to fabricate self-poled electrospun ferroelectric microfibers. For the first time, self-poling is reported to result from internal strain gradients achieved by supporting fibers on patterned, curved surfaces that induce upward flexoelectric self-poling.

The upward self-polarization is very robust and immune to external electrical (-54 V) and thermal (-100 to 70 oC) stimuli and was maintained for days. The authors also modeled and calculated the curving strain gradient and ferroelectric effect to demonstrate how bending of the fiber results in a strain gradient and upward self-polarization. In addition, nanogenerators fabricated from those self-poled fibers showed outputs comparable to the  onventionally poled devices. This work provides a promising solution to the well-known depolarization problem and demonstrates the fabrication of piezoelectric devices that are free from any poling process.