Influence of MWCNTs Length on the Ferroelectric and Piezoelectric Properties of PVDF-TrFE Composite Films

Multi-walled carbon nanotubes (MWCNTs) were employed as third-phase conductive fillers to explore their structural influence on the ferroelectric and piezoelectric characteristics of composite films. Departing from traditional physical mixing, this work adopted chemical vcapor deposition for the insitu growth of MWCNTs on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{BaTiO}_{3}$</tex> surfaces, enhancing their electrical coupling. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{BaTiO}_{3}$</tex> with different length of MWCNTs were incorporated into the PVDF-TrFE matrix, followed by complete characterization and performance testing. The findings reveal that short MWCNTs at a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5 \text{wt} {\%}$</tex> concentration improve the ferroelectric properties of composite films, boosting remnant polarization <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{r}$</tex> by 131% and lowering the coercive field <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E_{c}$</tex> from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$685 \text{kV} / \text{cm}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$585 \text{kV} / \text{cm}$</tex>, better meeting application's requirements such as those of F-RAM devices. The piezoelectric performance is improved, with the piezoelectric coefficient <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d_{33}$</tex> increasing by 62%, leading to higher output and sensitivity in piezoelectric sensors. In contrast, incorporating the same amount of longer MWCNTs creates a conductive network within the matrix, transforming the film into a conductive system unsuitable for ferroelectric and piezoelectric applications. Therefore, short MWCNTs at the right concentration are more effective in improving performance, although minor agglomeration still persists. Refining processing parameters to optimize MWCNTs length and dispersion could lead to further advancements in performance.