SrTiO₃/Epoxy Nanodielectrics as Bulk Energy Storage and Harvesting Systems: The Role of Conductivity

Abstract

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 (α-mode), (b) rearrangement of polar side groups (β-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 SrTiO 3 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.

Chemical composition tuning induced variable and enhanced dielectric properties of polycrystalline Ga2‐2xWxO3 ceramics

“…The commonly referred dielectric loss factor is defined as the ratio of imaginary part of dielectric constant to the real part and it is given by tan δ = ε ″/ ε ′, where δ is the phase difference between current and voltage of the applied electric field 57,63 . As shown in Figure 7, the loss factor with reference to change in temperature indicates that β ‐Ga 2 O 3 assumes a lower value for lower frequencies until temperatures of 350°C to 420°C.…”

“…The commonly referred dielectric loss factor is defined as the ratio of imaginary part of dielectric constant to the real part and it is given by tan = ′′ / ′ , where δ is the phase difference between current and voltage of the applied electric field. 57,63 As shown in Figure 7, the loss factor with reference to change in temperature indicates that -Ga 2 O 3 assumes a lower value for lower frequencies until temperatures of 350 • C to 420 • C. Then the loss tan rises exponentially toward the higher range of measuring temperatures. This is true for higher frequency range as well, indicating a dormant behavior of the participating species.…”

“…Which can be explanied by addressing the polarization source in the system. 57,58 At the lower end of the frequency range, ′ assumes higher values throughout the sweep profile. This is due to the fact that ionic, space charge and grain boundary polarization contribute to the higher values of ′ at lower frequencies.…”

“…The contribution of the interfacial losses and the loss from electrical conductivity (as discussed in the subsequent F I G U R E 6 The dependence of ′′ in GWO compounds as a function of W concentration at a particular frequency sections) is generally dominant at lower frequencies; however, these factors becomes negligible at higher frequencies. [55][56][57][58][59] Thus, the observed decrease in the imaginary part of the dielectric constant observed at higher frequencies can be attributed to the rapidly fading off the contributions from the interfacial as well as grain conductivity mechanisms. However, the large values -observed at lower frequency is mainly due to the W-doping induced complex chemistry of Ga 2 O 3 in terms of multiple valence cations, vacancies, and grain boundary defects.…”

“…However, the large values -observed at lower frequency is mainly due to the W-doping induced complex chemistry of Ga 2 O 3 in terms of multiple valence cations, vacancies, and grain boundary defects. 55,[57][58][59]…”