Fabrication and Characterization of Aligned Flexible Lead-Free Piezoelectric Nanofibers for Wearable Device Applications

Abstract

Flexible lead-free piezoelectric nanofibers, based on BNT-ST (0.78Bi_0.5Na_0.5TiO₃-0.22SrTiO₃) ceramic and poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) copolymers, were fabricated by an electrospinning method and the effects of the degree of alignment in the nanofibers on the piezoelectric characteristics were investigated. The microstructure of the lead-free piezoelectric nanofibers was observed by field emission scanning electron microscope (FE-SEM) and the orientation was analyzed by fast Fourier transform (FFT) images. X-ray diffraction (XRD) analysis confirmed that the phase was not changed by the electrospinning process and maintained a perovskite phase. Polarization-electric field (P-E) loops and piezoresponse force microscopy (PFM) were used to investigate the piezoelectric properties of the piezoelectric nanofibers, according to the degree of alignment-the well aligned piezoelectric nanofibers had higher piezoelectric properties. Furthermore, the output voltage of the aligned lead-free piezoelectric nanofibers was measured according to the vibration frequency and the bending motion and the aligned piezoelectric nanofibers with a collector rotation speed of 1500 rpm performed the best.

Keywords: aligned arrays; electrospinning; lead-free piezoelectric nanofiber; nanofiber composites; piezoelectric devices.

Figure 1

A schematic illustration of aligned dipoles in a polymer region and a ceramic region of the aligned piezoelectric nanofibers.

Figure 2

(a) Scanning electron microscope (SEM) images, Fast Fourier-transform (FFT) images and (b) nanofiber diameter distribution of BNT-ST nanofibers according to the rotation speed of the collector.

Figure 3

X-Ray Diffraction (XRD) patterns of the BNT-ST nanofibers according to the rotation speed of the collector.

Figure 4

Piezoresponse force microscopy (PFM) images, phase hysteresis loops and amplitude hysteresis loops of the BNT-ST nanofibers according to the rotation speed of the collector: (a) 0 rpm, (b) 500 rpm, (c) 1000 rpm and (d) 1500 rpm.

Figure 5

P-E hysteresis loops of the BNT-ST nanofiber modules according to the rotation speed of the collector. The inset shows maximum polarization values (P_max) according to the rotation speed of the collector.

Figure 6

The output voltage according to (a) vibration frequency and (b) bending motion for the BNT-ST nanofiber modules with different collector rotation speeds.