Solar energy is a major factor in the equation of energy, because of the unlimited potential of the sun that eclipses all other renewable sources of energy. Solar physical vapor deposition (SPVD) is a core innovative, original and environmentally friendly process to prepare nanocrystalline materials in a powder form. The principle of this process is to melt the material under concentrated solar radiation, which evaporates and condenses as nanopowders on a cold surface. We synthesized nanopowders of magnesium titanate by the SPVD process at PROMES Laboratory in Odeillo-Font Romeu, France. The SPVD system consists of a parabolic mirror concentrator, a mobile plane mirror (“heliostat”) tracking the sun and a solar reactor “heliotron”. The synthesized nanopowders were analyzed by X-ray diffraction (XRD) to know their crystalline structure and scanning electron microscopy (SEM) was used for determining the surface morphology. We have shown that the characteristics of obtained nanotitanates were determined by the targets’ composition and SPVD process parameters such as the working pressure inside the solar reactor and evaporation duration (process time).
Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputtering on Si/SiO2/Ti/Pt substrates. Once they were structurally characterized, the effect of oxygen vacancies on their electric properties was addressed by measuring leakage currents, dielectric constant, electric polarization, and thermally stimulated depolarization currents. By using K2O rich KTaO3 targets and specific deposition conditions, KTaO3-δ oxygen deficient thin films with a K/Ta = 1 ratio were obtained. Room temperature X-ray diffraction patterns show that KTaO3-δ thin films are under a compressive strain of 2.3% relative to KTaO3 crystals. Leakage current results reveal the presence of a conductive mechanism, following the Poole-Frenkel formalism. Furthermore, dielectric, polarization, and depolarization current measurements yield the existence of a polarized state below Tpol ~ 367°C. A Cole-Cole dipolar relaxation was also ascertained apparently due to oxygen vacancies induced dipoles. After thermal annealing the films in an oxygen atmosphere at a temperature above Tpol, the aforementioned polarized state is suppressed, associated with a drastic oxygen vacancies reduction emerging from annealing process.
Due to the increasing availability of substitute materials for electrical porcelain, research is needed to adapt formulations involving these materials to the current economic realities of the industry. This study assessed the effect of iron oxide concentration (0, 1, 2, 3, 5, and 8 wt%) on the dielectric properties of an aluminous porcelain composition commonly employed for electrical insulation based on different values of temperature and frequency. Samples with iron oxide contents of 0, 3, and 5 wt% were analyzed using dilatometry, X-ray diffraction, and scanning electron microscopy to evaluate the thermal, structural, and microstructural changes related to their Fe2O3 concentrations. Both the dielectric constant (εr) and the loss tangent (tanδ) were measured and evaluated in every sample. Results indicated that the presence of Fe2O3 increased the dielectric constant and loss tangent, which could result in an increase in heating by dielectric losses. Fe2O3 contents of up to 5 wt% had no significant effect on the performance of these insulators at room temperature (~30 °C) and a high frequency (1 MHz), especially when the hematite phase was completely solubilized in the porcelain phases.
Constrained sintering of BaLa4Ti4O15 (BLT) thick films on flexible platinum foil and on rigid BLT substrate showed enhanced grain growth and anisotropic microstructure development when compared with bulk samples having similar green packing and sintered under the same conditions. The evolution of the microstructural parameters (grain and pore shape, orientation) during densification and their correlation was investigated in films and compared with the morphological evolution in bulk samples. It is then expected that the appropriate choice of substrate will allow designing tailored microstructures of functional thick films with optimized performance.