Determining the dielectric constant of injection-molded polymer-matrix nanocomposites filled with barium titanate
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Research Letter
Determining the dielectric constant of injection-molded polymer-matrix nanocomposites filled with barium titanate Daniel Brito , Guadalupe Quirarte, Joshua Morgan, Eleanor Rackoff, Michael Fernandez, Dithi Ganjam, and Albert Dato , Department of Engineering, Harvey Mudd College, 301 Platt Blvd., Claremont, CA 91711, USA Todd C. Monson, Nanoscale Sciences Department, Sandia National Laboratories, 1515 Eubank Blvd., Albuquerque, NM 87123, USA Address all correspondence to Todd C. Monson at [email protected] (Received 12 June 2020; accepted 1 September 2020)
Abstract Barium titanate (BTO) is a ferroelectric perovskite with potential in energy storage applications. Previous research suggests that BTO dielectric constant increases as nanoparticle diameter decreases. This report recounts an investigation of this relationship. Injection-molded nanocomposites of 5 vol% BTO nanoparticles incorporated in a low-density polyethylene matrix were fabricated and measured. Finite-element analysis was used to model nanocomposites of all BTO sizes and the results were compared with experimental data. Both indicated a negligible relationship between BTO diameter and dielectric constant at 5 vol%. However, a path for fabricating and testing composites of 30 vol% and higher is presented here.
Introduction A material’s ability to store electrical energy at a particular voltage is dictated by its dielectric constant (ϵ), which defines the material’s permittivity relative to the permittivity of vacuum. The increasing demand for energy storage has driven research into superior dielectrics, referred to as colossal dielectric constant (CDC) materials.[1,2] These materials have dielectric constants above 1000, which is much higher than that of conventional dielectrics, such as plexiglass, mica, and air.[3] The most common mechanisms that can give rise to these large values of the dielectric constant are ferroelectricity, charge–density wave formation, hopping charge transport, and various kinds of interface effects.[2] The ferroelectric perovskite compound BaTiO3 (BTO) is a CDC material. As shown in Supplementary Fig. S1, the structure of BTO consists of a central titanium atom that is slightly offset from the unit cell midplane (when below the Curie temperature), resulting in a relatively high dielectric constant at room temperature.[4–6] BTO has a generally accepted dielectric constant between 1500 and 2000 for particle diameters of 1 μm.[7] Multiple studies have demonstrated the dependence of the dielectric constant of BTO on particle diameter, and BTO nanoparticles with diameters lower than 500 nm have exhibited dielectric constants as high as 4000.[8] In one study, the dielectric constants of BTO nanoparticles synthesized in a vacuum environment were investigated.[9] Across a particle diameter range of 10–500 nm, a dramatic increase in dielectric constant to over 15,000 was reported for BTO with a diameter of ∼70 nm.[9] A similar peak in dielectric constant was found for BTO
nanoparticles produced in air.[10] Promising
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