Controlled Synthesis of BaTiO3 Nanofibers for Enhanced Piezoelectric Properties

Abstract

Reducing the size of piezoelectric energy harvesting devices – progressing from bulk materials, through the micro scale, and now into the nanoscale – is attracting interest in new size-based classifications of clean energy sources converting ambient, attenuated mechanical energy into electrical energy. Compared to the macro devices, nanostructures based transducer materials, with their exclusively large surface area-to-volume ratio, have shown enhanced piezoelectric properties. In this paper, electrospinning was used to fabricate nanofibrous structures by jetting a solution of barium and titanium precursors dissolved in poly (vinyl pyrrolidone) (PVP) with an applied voltage. Three separate full-factorial design of experiments (DOEs) (one 3-level, two 2-levels) were conducted to control and optimize the process to minimize fiber diameter with the least amount of beading defects. The three factor design focused on the optimization of the solution properties (viscosity, electrical conductivity, surface tension), one of the two factors focused on electrospinning parameters (voltage, flow rate), and the other on environmental conditions (temperature, absolute humidity). The viscosity was controlled by the polymer weight percentage, the electrical conductivity controlled by the salt to polymer ratio, and the surface tension controlled by the solvent. Low temperature and low absolute humidity produced the smallest fibers. Scanning electron microscopy (SEM) was utilized to characterize the morphology and diameter of the as-spun nanofibers. Micrographs of our best results showed as-spun nanofibers with an average diameter of 74.6 ± 15 nm with minimal beading. The as-spun nanofiber mats were subsequently calcinated and annealed to produce BaTiO3 nanofibers to be tested for their piezoelectric properties.