Measuring the Permittivity of Ferroelectric Nanoparticles in an Epoxy Composite

Sandia National Laboratories

Barium titanate, or BTO, is widely used as a dielectric material due to its high dielectric constant, which typically ranges from 1500 to 2000 in bulk. Despite its prevalence as a dielectric material, current literature remains unclear on how BTO nanoparticle size impacts the dielectric constant, particularly for non-sintered, discrete nanoparticles. Other research groups have reported BTO nanoparticle dielectric constants ranging from 135 to 5000, with no indication of the uncertainty. Our team previously attempted to measure the dielectric constant of BTO nanoparticles by loading them in an epoxy composite, measuring the effective dielectric constant of the mixture, and using COMSOL modeling to extract the dielectric constant of the nanoparticles themselves. Experimental observations and additional COMSOL modeling indicated that agglomeration of BTO nanoparticles within the composites raised the effective dielectric constant such that determination of the BTO nanoparticle dielectric constant was impossible using our existing methods.

In order to overcome the agglomeration issue and allow for the extraction of the BTO nanoparticle dielectric constant, we developed a ball-milling procedure to eliminate BTO nanoparticle agglomerates before loading them into the epoxy. We examined two volume fractions of BTO that can be achieved with this procedure, and were  able to determine the dielectric constant of 500 nm BTO nanoparticles in a 20% volume loading composite to be 225 ± 75 for our nanoparticles, assuming 0% agglomeration. Finally, we also developed more robust COMSOL models for understanding the effects of BTO agglomerate size on the effective dielectric constant.

Advisor(s): Albert Dato and Richard Campbell Haskell.

Team: Isabel Ann Martos-Repath ’18, Marisol Nora Beck ’17, Jonas Leif Kaufman ’17, Cesar Jose Orellana ’17, Carmel Jia Zhao ’17, and Robin Bendiak ’17.