A strategy for design of non-percolative composites with stable giant dielectric constants and high energy densities

Abstract

Materials with high dielectric constants can be fabricated into electrostatic capacitors for energy storage. Traditional percolative dielectrics such as epoxy/Ag and BaTiO3/Ni have limited energy densities due to the limited breakdown strengths. Here, a strategy for design of non-percolative composites is reported having stable giant dielectric constants and high breakdown strengths simultaneously, and thus, exhibiting high energy densities. A composite is fabricated by using a core-shell type Ag@BaTiO3 fillers where the BaTiO3 shell helps to completely separate the Ag cores with other cores in a sintered BaTiO3 matrix. The composite possesses a stable giant dielectric constant (εr~51,800, εr/εm = 15.6) over wide ranges of frequencies and temperatures while retaining a small dielectric loss (tanδ < 0.02) and a high breakdown strength (Eb > 43 kV cm–1). With the giant εr and the high Eb, the composite exhibits a high energy density (Ue~4.35 J cm–3) which is much enhanced compared with that of percolative composites and neat BaTiO3. Our comparative study with existing composite models reveals that the dielectric behavior in this composite is governed by an interfacial polarization mechanism rather than the power law for percolative dielectrics. This study successfully demonstrated very high k, Eb and energy density of a BT composite by incorporating Ag@BaTiO3 core-shell fillers.