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Enhanced Dielectric Properties of LaNiO3/BaTiO3/PVDF: A Three-Phase Percolative Polymer Nanocrystal Composite

Jaschin, P. W., Bhimireddi, R., Varma, K. B. R.
ACS applied materials & interfaces 2018 v.10 no.32 pp. 27278-27286
barium titanate, dielectric properties, fluorides, lanthanum, nanocrystallites, polymers, transmission electron microscopy
Polymer (poly(vinylidene fluoride) (PVDF)) nanocrystal composites based on lanthanum nickelate (percolative oxide) and barium titanate were fabricated to obtain material systems with a high dielectric constant and low loss to be used for high-charge-storage applications. Lanthanum nickelate (LaNiO₃) nanocrystallites were synthesized from a simple citrate-assisted sol–gel route that yielded agglomerated crystallites of an average size of 120 nm. The defective nature of the lanthanum nickelate nanocrystals was revealed by the transmission electron microscopy studies. Hot-pressing method was executed to fabricate the LaNiO₃/PVDF nanocrystal composites, and their dielectric characteristics showed a low percolation threshold in the region of fLN (volume fraction of lanthanum nickelate) = 0.10. The percolative conductive filler–polymer nanocrystal composite at the percolation threshold exhibited a dielectric constant (εᵣ) and loss (D) of 55 and 0.263, respectively, at 10 kHz; the dielectric constant obtained was more than 5 times that of host matrix PVDF. To further improve upon the obtained dielectric properties from the two-phase composites, a high-dielectric-constant material, barium titanate (BaTiO₃) nanocrystals, with an average size of 100 nm, was embedded in the polymer matrix as the third phase. The dielectric properties of the three-phase nanocrystal composites were measured as a function of the volume fraction of lanthanum nickelate (which was limited within the percolation threshold), and a dielectric constant as high as 90 and the associated loss of 0.13 at 10 kHz were achieved from fLN = 0.09 and fBT = 0.20. The obtained dielectric constant from this system is 9 times more than that of PVDF and 3 times that of a two-phase barium titanate/PVDF composite, which proves to be a promising material for charge-storage applications.