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

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 f_LN (volume fraction of lanthanum nickelate) = 0.10. The percolative conductive filler-polymer nanocrystal composite at the percolation threshold exhibited a dielectric constant (ε_r) 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 f_LN = 0.09 and f_BT = 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.