Nanoparticle boost for capacitors

A new technique for creating films of barium titanate (BaTiO3) nanoparticles in a polymer matrix could allow fabrication of improved capacitors able to store twice the energy of existing devices. The improved capacitors could be used in consumer devices such as mobile phones and in defence applications requiring both high-energy storage and rapid current discharge.



Because of its high dielectric properties, barium titanate has long been of interest for use in capacitors, but until recently materials scientists had been unable to produce good dispersion of the material within a polymer matrix. By using tailored organic phosphonic acids to encapsulate and modify the surface of the nanoparticles, researchers at the Georgia Institute of Technology’s Centre for Organic Photonics and Electronics were able to overcome the particle dispersion problem to create uniform nanocomposites.



The new nanocomposite materials have been tested at frequencies of up to one megahertz, and even higher frequencies may be possible. Though the new materials could have commercial application without further improvement, their most important contribution may be in demonstrating the new encapsulation technique, which could have broad applications in other nanocomposite materials.



Because of their ability to store and rapidly discharge electrical energy, capacitors are used in a variety of consumer products such as computers and mobile phones. And because of the increasing demands for electrical energy to power vehicles and new equipment, they also have important military applications.



Key to developing thin-film capacitor materials with higher energy storage capacity is the ability to uniformly disperse nanoparticles in as high a density as possible throughout the polymer matrix. However, nanoparticles such as barium titanate tend to form aggregates that reduce the ability of the nanocomposite to resist electrical breakdown.



The Georgia Tech research team used organic phosphonic acids to encapsulate the particles. The tailored organic phosphonic acid ligands provide a robust coating for the particles, which range in size from 30 to 120 nanometres in diameter.



Though large crystals of barium titanate could also provide a high dielectric constant, they generally do not provide adequate resistance to breakdown, and their formation and growth can be complex and require high temperatures. Composites provide the necessary electrical properties, along with the advantages of solution-based processing techniques.



According to the researchers, there are many areas beyond capacitors where high dielectric materials are important, such as field-effect transistors, displays and other electronic devices. With our material, we can provide a high dielectric layer that can be incorporated into those types of applications.