Effects of Ni particle size on dielectric properties of PMMA-Ni-BaTiO ₃ composites

PMMA-Ni and PMMA-Ni-BaTiO₃ composites were fabricated by a two-step mixing and hot-molding method. The effects of the Ni particle size on the dielectric behaviors of the composites were examined. When small Ni particles (4 μm) were used as a filler in the PMMA-Ni and PMMA-Ni-BaTiO ₃ composites, the dielectric constant of the composites started to increase at the lower volume fraction of the Ni particles than that of the composites with larger Ni particles (40 μm). The percolation power law in the smearing region was employed to explain the experimental results. The critical exponents for the dielectric constant, dielectric loss, and direct current conductivity of the composites depended on the particles size of Ni and the volume fraction of BaTiO₃ particles. Smaller Ni particles with the same volume faction of BaTiO₃ in the composites yielded the smaller critical exponents. The small critical exponents mean that the increasing rates of the dielectric constant and loss of the composites near the percolation threshold are small and that the smearing regions are large.