Measurement of BTO Nanoparticle Permittivity in Stable Dispersions
Sandia National Laboratories
Barium titanate (BTO) nanoparticles exhibit intriguing size-dependent structural and dielectric properties which make them a candidate for use in novel capacitor technologies. This year, Sandia National Laboratories has once again engaged a clinic team (SNL Ferroelectric 2013-14) at Harvey Mudd College to explore BTO nanoparticle behavior. Building upon last year‘s results, the current SNLFE clinic team has worked to finalize and implement a procedure for measuring the dielectric constant of BTO nanoparticles in stable dispersions by electrochemical impedance spectroscopy (EIS). We have investigated the effects of sonication on dispersion stability for a range of BTO/solvent slurries, finding highly stable slurries of 50 nm Sakai KZM-50 series particles for low BTO loadings. Alternately, we successfully imbed BTO nanoparticles in an ULTEM polymer matrix at volume fractions up to 10%. In addition, we have measured the permittivity of 1 vol% to 10 vol% BTO slurries with high reproducibility (roughly 3% variation in permittivity between samples). However, our numerical models have revealed an extreme sensitivity of the calculated average particle permittivity to the measured overall dispersion permittivity.
We have also begun to probe the structure and ferroelectric behavior of BTO nanoparticles of different sizes and syntheses using a variety of spectroscopic, microscopic, and diffraction methods. For nanoparticles of 50 nm in diameter and smaller, preliminary atomic pair distribution function measurements confirm the absence of a sharp transition from tetragonal to cubic structure at the bulk Curie temperature. This lack of transition is in agreement with both the 2012-2013 and 2013-2014 Raman measurements, while in stark opposition to prior XRD measurements which indicate a cubic structure at all temperatures. These results suggest phase decoherence in smaller nanoparticles, which we speculate may be due to surface lattice distortions.
Advisor(s): Richard Campbell Haskell and Adrian Hightower.
Team: Robert G. Gambee ’15, Sun Hwi Bang ’14, Nathaniel (Nate) J. Bean ’14, and Jean-Claude David de Sugny ’14.