Anna STEPANOVA

The present study investigates the influence of strontium (Sr) content on the intrinsic properties of barium strontium titanate (Ba1-xSrxTiO3, BST) which was successfully prepared by the conventional solid-state reaction with different concentrations of strontium (x = 0, 0.3, 0.5, 0.6, 0.7, 1). The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and diffuse reflectance spectroscopy, the dielectric properties being also investigated. Structural and vibrational analyses reveal a structural phase transition from tetragonal to cubic at x = 0.4, with a linear decline of the tetragonality ratio as well as a shrinkage in the unit cell volume that occur with increasing Sr content. The morphological study shows that the grain size decreases as the Sr content increases in the tetragonal phase. Yet, upon the phase transition from tetragonal to cubic, the grain size initially increases, followed by a subsequent decrease with further Sr addition. It has been found that the band gap shows a decrease as Sr content increases. The temperature dependence of the dielectric parameters reveals that the Curie temperature as well as the dielectric constant and the loss tangent are strongly affected by the addition of Sr. The activation energy derived from the dielectric response, was found to be in the range 0.685-1.065eV, suggesting the dominance of doubly ionized oxygen vacancy for conduction and relaxation mechanism. Ab initio calculations were done employing the Linear Combination of Atomic Orbitals (LCAO) method. The bandgap energy (Eg) and the structural parameters were calculated using various types of exchange-correlation functionals (PWGGA, PBE, B3LYP and PBE0). A good agreement with the experimental results is achieved using the PBE0 functional. This study contributes to a better understanding of the structure-property relationship in BaSrTiO3 and provides valuable insights for optimizing its performance in various technological applications.

The present study investigates the influence of strontium (Sr) content on the intrinsic properties of barium strontium titanate (Ba1-xSrxTiO3, BST) which was successfully prepared by the conventional solid-state reaction with different concentrations of strontium (x = 0, 0.3, 0.5, 0.6, 0.7, 1). The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and diffuse reflectance spectroscopy, the dielectric properties being also investigated. Structural and vibrational analyses reveal a structural phase transition from tetragonal to cubic at x = 0.4, with a linear decline of the tetragonality ratio as well as a shrinkage in the unit cell volume that occur with increasing Sr content. The morphological study shows that the grain size decreases as the Sr content increases in the tetragonal phase. Yet, upon the phase transition from tetragonal to cubic, the grain size initially increases, followed by a subsequent decrease with further Sr addition. It has been found that the band gap shows a decrease as Sr content increases. The temperature dependence of the dielectric parameters reveals that the Curie temperature as well as the dielectric constant and the loss tangent are strongly affected by the addition of Sr. The activation energy derived from the dielectric response, was found to be in the range 0.685-1.065eV, suggesting the dominance of doubly ionized oxygen vacancy for conduction and relaxation mechanism. Ab initio calculations were done employing the Linear Combination of Atomic Orbitals (LCAO) method. The bandgap energy (Eg) and the structural parameters were calculated using various types of exchange-correlation functionals (PWGGA, PBE, B3LYP and PBE0). A good agreement with the experimental results is achieved using the PBE0 functional. This study contributes to a better understanding of the structure-property relationship in BaSrTiO3 and provides valuable insights for optimizing its performance in various technological applications.

Interest in self-cleaning coatings is rising due to their potential to enhance comfort and quality of life in polluted urban environments, driving the search for materials with optimal physical properties. Convergent with this goal, this study investigates the wetting properties and photo-catalytic efficiency of reticulated TiO2 layers. It shows that these properties are significantly influenced by the topographical characteristics of the TiO2 surface, which can be precisely controlled through variations in pulverization pressure and low-temperature post-annealing treatments. Post-deposition annealing of the TiO2 layers achieves 100 % self-cleaning efficiency for both thick and thin films, with optical transmission ranging from approximately 60 %-80 % in the visible spectrum. Additionally, the TiO2 layers exhibited promising capabilities for eliminating pathogenic microorganisms and disinfecting surfaces. The underlying causal factors of these remarkable and technologically promising surface features are explored and discussed.

Photocatalysis is one of the approaches for solving environmental issues derived from extremely harmful pollution caused by industrial dyes, medicine, and heavy metals. Titanium dioxide is among the most promising photocatalytic semiconductors; thus, in this work, TiO2 powders were prepared by a hydrothermal synthesis using titanium tetrachloride TiCl4 as a Ti source. The effect of the hydrochloric acid (HCl) concentration on TiO2 formation was analyzed, in which a thorough morpho-structural analysis was performed employing different analysis methods like XRD, Raman spectroscopy, SEM/TEM, and N-2 physisorption. EPR spectroscopy was employed to characterize the paramagnetic defect centers and the photogeneration of reactive oxygen species. Photocatalytic properties were tested by photocatalytic degradation of the rhodamine B (RhB) dye under UV light irradiation and using a solar simulator. The pH value directly influenced the formation of the TiO2 phases; for less acidic conditions, the anatase phase of TiO2 crystallized, with a crystallite size of approximate to 9 nm. Promising results were observed for TiO2, which contained 76% rutile, showing a 96% degradation of RhB under the solar simulator and 91% under UV light after 90 min irradiation, and the best result showed that the sample with 67% of the anatase phase after 60 min irradiation under the solar simulator had a 99% degradation efficiency.