Influence of Ferroelectric Filler Size and Clustering on the Electrical Properties of (Ag-BaTiO₃)-PVDF...

The paper presents a study concerning the role of ferroelectric filler size and clustering in the dielectric properties of 20%BaTiO₃-80%PVDF and of 20% (2%Ag-98%BaTiO₃)-PVDF hybrid nanocomposites. By finite element calculations, it was shown that using fillers with ε > 10³ does not provide a permittivity rise in the composites and the effective dielectric constant tends to saturate to specific values determined by the filler size and agglomeration degree. Irrespective of the ferroelectric filler sizes, the addition of metallic ultrafine nanoparticles (Ag) results in permittivity intensification and the effect is even stronger if the metallic nanoparticles are connected to a higher degree with the ferroelectric particles' surfaces. When using coarse ferroelectric fillers, the probability of clustering is higher, thus favoring the permittivity increase by field concentration in small regions close to the interfaces separating dissimilar materials. The modeling results were validated by an experimental dielectric analysis performed in a series of PVDF-based thick films with the same amount of BaTiO₃ fillers or with Ag-BaTiO₃ hybrid fillers. Similar trends as predicted by simulations were found experimentally but with slightly higher permittivity values which were assigned to the modifications of the polymer phase composition due to the presence of nanofillers and the local sample inhomogeneity (the presence of clustering, in particular for coarse BaTiO₃ grains), which create regions with enhanced local fields.