High dielectric properties in a three-phase polymer composite induced by a parallel structure

A novel three-phase composite, consisting of semiconductive bismuth sulfide (Bi2S3) nanorods and self-passivated aluminum flakes (AFs)1 embedded in a poly(vinylidene fluoride) (PVDF) matrix, was fabricated by simple but robust ball-milling and hot-pressing techniques. The dielectric properties of composites were studied before and after the addition of AFs as a function of Bi2S3 volume fraction and frequency. The Bi2S3 nanorods in PVDF matrix form a percolation path and increase the dielectric constant of the composite dramatically. And after adding the third phase AFs, a parallel structure forms during the hot-pressing progress. Parallel AFs in the PVDF matrix can largely reduce the leakage current due to the self-passivated insulating shell outside the AFs, thus an obvious reduction in the dielectric loss of the three-phase Bi2S3–AFs/PVDF composite is observed. Meanwhile, many microcapacitors formed with Al flakes as electrodes and Bi2S3/PVDF composite as the dielectric layer form, which makes an additional contribution to the high dielectric constant of the three-phase composite.

► Aluminum flakes form a parallel structure in polymer matrix.
► The dielectric loss is largely lower after the addition of self-passivated AF.
►  Parallel structure is helpful for composite to maintain a high dielectric constant.