Microwave-absorbing
materials have attracted enormous attention
for electromagnetic (EM) pollution. Herein, hollow beaded Fe3C/N-doped carbon fibers (Fe3C/NCFs) were synthesized through
convenient electrospinning and subsequent thermal treatment. The special
hollow morphology of the samples is conducive to achieve lightweight
and broadband microwave absorption properties. The thermal treatment
temperatures exhibit a significant impact on conductivity and EM properties.
The broadest effective absorption bandwidth (EAB) is 5.28 GHz at 2.16
mm when the thermal treatment temperature is 700 °C, and the
EAB can cover 13.13 GHz with a tunable absorber thickness from 1.0
to 3.5 mm when the thermal treatment temperature is 750 °C. The
excellent microwave absorption properties of the samples are due to
the synergistic effect of impedance matching and strong EM energy
attenuation abilities. Hence, the magnetic hollow beaded Fe3C/NCFs are expected to be an attractive candidate material as a lightweight
and efficient microwave absorber in the future.
Cooling based on the electrocaloric effect (ECE) is a promising solution to environmental and energy efficiency problems of vapor-compression refrigeration. Ferroelectric polymer-ceramics nanocomposites, integrating high electric breakdown of organic ferroelectrics and large EC strength of ceramics, are attractive EC materials. Here, we tuned the orientation of Ba 0.67 Sr 0.33 TiO 3 nanofibers (BST nfs) in the P(VDF-TrFE-CFE) polymer. When the nfs were aligned parallel to the field, a ΔT of 11.3 K with an EC strength of 0.16 K•m/MV was achieved in the blends. The EC strength not only surpasses advanced nanocomposites but also is comparable to ferroelectric ceramics. The simulation indicates that a significantly higher electric field is concentrated in polymer regions around the ends of the orientated nfs, contributing to easier flipping of polymer chains for large ECE. This work provides a new method to obtain large ECE in composites for next-generation refrigeration.
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