BaTiO3 is one of the most widely used ceramic components in capacitor formulation due to its exceptional ferroelectric properties. The structural transition from the ferroelectric tetragonal to the paraelectric cubic phase has been studied in both nano- and micro-BaTiO3 particles. Several experimental techniques were employed for characterization purposes (X-ray diffraction-XRD, laser Raman spectroscopy-LRS, differential scanning calorimetry-DSC and broadband dielectric spectroscopy-BDS). All gave evidence for the structural transition from the polar tetragonal to the non-polar cubic phase in both nano- and micro-BaTiO3 particles. Variation of Full Width at Half Maximum (FWHM) with temperature in XRD peaks was employed for the determination of the critical Curie temperature (Tc). In micro-BaTiO3 particles (Tc) lies close to 120 °C, while in nanoparticles the transition is complicated due to the influence of particles’ size. Below (Tc) both phases co-exist in nanoparticles. (Tc) was also determined via the temperature dependence of FWHM and found to be 115 °C. DSC, LRS and BDS provided direct results, indicating the transition in both nano- and micro-BaTiO3 particles. Finally, the 15 parts per hundred resin per weight (phr) BaTiO3/epoxy nanocomposite revealed also the transition through the peak formation at approximately 130 °C in the variation of FWHM with temperature. The present work introduces, for the first time, a qualitative tool for the determination and study of the ferroelectric to paraelectric structural transition in both nano- and micro-ferroelectric particles and in their nanocomposites. Moreover, its novelty lies on the effect of crystals’ size upon the ferroelectric to the paraelectric phase transition and its influence on physical properties of BaTiO3.

Barium titanate/epoxy resin composite nanodielectrics were manufactured and their capability to store and harvest energy, upon request under DC conditions, was studied in this work. Morphological characterization in all nanocomposites was performed via scanning electron microscopy images and X-ray diffraction spectra, indicating the successful nanofiller's integration and dispersion within the polymer matrix. Applied DC voltage level varied from 10 to 240 V and the measurements were performed in the temperature range from 30 to 160°C. Filler content enhances the energy efficiency of the manufactured systems, reaching the highest value of 58.2% for the 7 phr BaTiO 3 nanocomposite. Increase of temperature results in an exponential decay of the coefficient of energy efficiency (n eff), indicating leakage currents' augment. DC and AC conductivity have been determined as a function of temperature for all nanodielectric systems. The temperature dependence of conductivity under DC and AC condition follows an Arrhenius form, which allowed the determination of activation energy in both cases.

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.

Composite nanodielectrics consisted of an epoxy resin and barium titanate nanoparticles were developed and characterised. Electrical measurements were performed via broadband dielectric spectroscopy. Dielectric results reveal the presence of three relaxation 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 polarisation between system's constituents. The ability of the examined nanodielectrics to store and harvest energy was also examined in dc conditions. Applied dc voltage varied in the range of 10-240 V. Experimental data indicate that increasing the applied dc field results to higher values of the stored and harvested energies. The energy efficiency was also investigated in all specimens. The filler content enhances the coefficient of energy efficiency (n eff) up to 58.2% for the 7 phr BaTiO 3 nanocomposite at 200 V and 10 s charging/discharging time.