Enhanced dielectric constant of polymer-matrix compositesusing nano-BaTiO₃ agglomerates

The epoxy/matrix composites incorporating with dispersed and agglomerated nano-BaTiO₃ fillers were investigated. The relative dielectric constants of the composites with the agglomerated particles were significantly improved, compared to those of the composites with the well-dispersed particles. In addition, the experimental data were in better agreement with the values calculated by the Lichteneker's model than with those of the conventional Maxwell-Garnett's model which has been widely employed for the calculation of the dielectric constant of polymer/filler composites. In order to promote an agglomeration by interlocking between the nanoparticles, the BaTiO₃ powders were heat-treated at various temperatures. An epoxy composite with 40 vol% BaTiO₃ heat-treated at 800°C for 1 h exhibited an excellent relative dielectric constant of 67, along with high polarizability, low dielectric loss, and low leakage current. Similarly, the epoxy composites with agglomerated SrTiO₃ fillers provided a higher dielectric constant than that of their dispersed counterparts. The origin of the increase in the relative dielectric constant achieved by the agglomeration effect is also suggested.