CoFe^sub 2^O^sub 4^ nanofiller effect on ß-phase formation of PVDF matrix for polymer-based magnetoelectric composites

In this study, we systematically investigated the effects of CoFe2O4 (CFO) nanofillers on the β-phase formation of piezoelectric PVDF after solvent casting, thermal annealing, electrical poling, and uniaxial stretching, which are all essential steps in the fabrication of magnetoelectric composites. Therefore, zero-dimensional CFO nanoparticles and one-dimensional CFO nanorods were prepared as magnetostrictive nanofillers via hydrothermal synthesis. Among three-type films consisting of PVDF, PVDF/CFO nanoparticles, and PVDF/CFO nanorods, the β-phase fractions of PVDF were found to exhibit the maximum values of 47.1 after poling and 78.5% after stretching, in the films of PVDF/CFO nanoparticles. These results illustrated that the shape and size of CFO nanofillers are very important for the design of polymer-based magnetoelectric composites, because the nanofillers are beneficial to provide a physical barrier that helps maintain parallel dipoles of the β-phase, while simultaneously playing the negative role of conductors to induce electrical percolation.