SrTiO3/Epoxy Nanodielectrics As Bulk Energy Storage and Harvesting Systems: the Role of Conductivity

Composite nanodielectric materials with strontium titanate nanoparticles embedded within an epoxy resin matrix were prepared and studied, varying the filler content. Broadband dielectric spectroscopy was employed for determining the dielectric response of the prepared specimens. Dielectric results reveal the presence of three relaxations processes, which are attributed to (a) glass to rubber transition of the polymer matrix (alpha-mode), (b) rearrangement of polar side groups (beta-mode), and (c) interfacial polarization between systems' constituents. The stored and harvested energy of the examined nanodielectrics was also evaluated under DC conditions in the applied voltage range of 10-240 V. The coefficient of energy efficiency (n(eff)) was determined for all filler's content, varying the applied temperature and field. The effect of temperature appears to be pronounced, causing a sigmoidal dependence of n(eff). Furthermore, filler content enhances n(eff), reaching the highest value of 69.41% for the 10 phr SrTiO3 nanocomposite at 50 V. Finally, both AC and DC conductivities were evaluated as a function of filler and temperature, and the corresponding activation energies were calculated. Hopping conductivity appears to be the predominant conduction mechanism in all nanocomposite systems, since experimental data are in accordance with variable range hopping model.