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Four iron-based triple tungstate and tellurate perovskites have been synthesized in the nanocrystalline form using a simple sol–gel citrate route: Sr3Fe2WO9 (SFWO), Ba3Fe2WO9 (BFWO), Sr3Fe2TeO9 (SFTO), and Ba3Fe2TeO9 (BFTO). Strontium-based compounds crystallize in the tetragonal space group I4/m, while barium-based compounds crystallize in the hexagonal space group P63/mmc. All compounds possess a ferromagnetic order with high values for room-temperature magnetization. The magnetic state as traced by Mössbauer spectroscopy is heterogeneously related to disorder. The compounds also possess relatively high dielectric constants (20–199.16) measured at 1 MHz and a moderate loss factor. The synthesized triple perovskite compounds were utilized in the fabrication of vertical contact mode triboelectric nanogenerators (TENGs). The working mechanism and the electrical response of the TENGs were extensively studied. The TENG device based on BFTO/Kapton triboelectric layers produces the highest output of 88 V/2.69 μA. For the first time, the surface polarity of the triple perovskite was shown using a Kelvin probe force microscopy technique (KPFM), which elucidates the positive polarity of the triboelectric layer. Furthermore, the TENG device was used to charge several capacitors and to carry out the powering of electronics that make it an excellent choice for various self-powered applications.

In this study, clay composites were subjected to electromagnetic transmission testing at frequencies in the region of non-ionizing radiation. Specimens were made with partial substitution of clay with different admixtures by mass. Admixtures used were Fly Ash, four different particle sizes and phases of Titanium Dioxide (TiO2), Zinc Ferrite (ZnFe2O4), Maghemite (γ-Fe2O3) and Antimony Tin Oxide (ATO). The additives were thoroughly (chemically, structurally, morphologically) characterized. The replacement percentage was 5 wt.%. Electromagnetic transmission assessment included S21 transmission coefficient measurements for samples with different additives. The lowest transmission was reported for the clay specimens with ATO and Titanium Dioxide, especially at higher frequencies. A decrease in the transmission parameter with increasing specimen thickness was also confirmed.

The main objective of this work was to synthesize phase pure double perovskites Ba2NiTeO6 (BNTO) and Ba2NiWO6 (BNWO) in nanocrystalline form and to reveal the impact of nanocrystallinity on their magnetic and dielectric properties. The studied double perovskites were synthesized in nanocrystalline form by employing a citrate sol-gel route. A detailed investigation of their structure and properties using X-ray powder diffraction, scanning electron microscopy, Raman spectroscopy technique, energy-dispersive X-ray spectroscopy, SQUID magnetometry and electrical measurements is carefully described. Rietveld refinement of X-ray powder diffraction patterns revealed phase purity of both compounds: BNTO is trigonal (R-3m) while BNWO is cubic (Fm-3m). Raman spectroscopy studies reveal optical phonons that correspond to vibrations of Te6+/W6+O6 octahedra, while scanning electron microscopy images show irregular plate-like nanocrystals. Magnetic property measurements speak in favor of antiferromagnetic order but, in both compounds, size reduction affected their properties. BNTO has Néel temperature (TN) of 10.3 K which is higher than previously reported for its bulk form. Magnetic ground state of BNWO can be explained as canted antiferromagnetism with TN = 48.2 K. Room temperature measurements of dielectric constants at various frequencies suggest that these materials are high-κ dielectrics with low dielectric loss. The Nyquist plot reveals depressed a semicircle arc typical for non-Debye type of relaxation phenomena for BNWO ceramic, whereas for BNTO ceramic an almost straight line of Zʹʹ versus Z' has been observed, indicating its high insulating behavior. To conclude, size-dependent properties of studied double perovskites are discussed, introducing a possibility for implementation in electronic devices.

Five different rare-earth-based nanocrystalline high entropy oxides (HEOs) with fluorite type of structure and average crystallite sizes between 6 and 8 nm were prepared and their photocatalytic behaviour towards AZO dye degradation and photoelectrochemical water splitting for hydrogen generation was examined. The cationic site in the fluorite lattice consists of five equimolar elements selected from the group of rare-earth elements including La, Ce, Pr, Eu, and Gd, and second-row transition metals, Y and Zr. Studied HEOs exhibit bandgaps in the range from 1.91 eV to 3.0 eV and appropriate valence and conduction bands for water splitting. They reveal high photocatalytic activity that is mostly attributed to the accessibility of more photocatalytic active sites which provided radicals responsible for the AZO dye degradation. The materials successfully produce hydrogen by photocatalytic water splitting, suggesting the potential of HEOs as new photocatalysts. The photocatalytic performances of all studied HEOs outperform the single fluorite oxides or equivalent mixed oxides. The Ce0.2Zr0.2La0.2Pr0.2Y0.2O2 (CZLPY) engender hydrogen in 9.2 µmolmg–1 per hour which is much higher content than for pristine CeO2 material which amounts to 0.8 µmolmg–1 per hour.

Adsorption of polymers on mineral surfaces is of great importance in many industry branches and applications. Physico-chemical properties of polymers, substrates and general suspensions determine the adsorption at the solid / liquid phase boundary. The properties and structures of the polymer depend on the kinetics and the balance of adsorption processes. The paper deals with the adsorption of poly (acrylic) acids of different molecular masses on aluminum oxide and silicon carbide at different pH values. Aluminum oxide samples had the same mineralogical composition, but different porosity. Solid, porous aggregates made of fine crystals were characterized by application of raster electron microscope (SEM), and particle porosity was determined by adsorption of nitrogen (B.E.T.) and mercury porosimetry. Molecular dimensions of poly (acrylic) acids have been calculated in different conformations depending on pH: coiled and stretched. It has been found that the adsorption density is growing on the nephrotic surface and significantly decreases when the molecular mass increases when the particle surface is porous (at pH less than 7). In acidic suspensions, poly (acrylic) acid is largely not ionized and the adsorption surface available depends on the size of the polymer molecule. Tests have shown that when adsorption of polyacrylic acid on silicon carbide plates changes the ζ potential. It is known that aluminum oxide and silicon carbide are common ceramic materials and the results of this work can contribute to the development of different techniques for the production of various ceramic materials based on colloidal chemistry.

Double perovskites have been extensively studied in materials chemistry due to their excellent properties and novel features attributed to the coexistence of ferro/ferri/antiferro-magnetic ground state and semiconductor band gap within the same material. Double perovskites with Sr2NiMO6 (M = Te, W) structure type have been synthesized using simple, non-toxic and costless aqueous citrate sol-gel route. The reaction yielded phase-pure nanocrystalline powders of two compounds: Sr2NiWO6 (SNWO) and Sr2NiTeO6 (SNTO). According to the Rietveld refinement of powder X-ray diffraction data at room temperature, Sr2NiWO6 is tetragonal (I4/m) and Sr2NiTeO6 is monoclinic (C12/m1), with average crystallite sizes of 49 and 77 nm, respectively. Structural studies have been additionally performed by Raman spectroscopy revealing optical phonons typical for vibrations of Te6+/W6+O6 octahedra. Both SNTO and SNWO possess high values of dielectric constants (341 and 308, respectively) with low dielectric loss (0.06 for SNWO) at a frequency of 1 kHz. These values decrease exponentially with the increase of frequency to 1000 kHz, with the dielectric constant being around 260 for both compounds and dielectric loss being 0.01 for SNWO and 0.04 for SNTO. The Nyquist plot for both samples confirms the non-Debye type of relaxation behavior and the dominance of shorter-range movement of charge carriers. Magnetic studies of both compounds revealed antiferromagnetic behavior, with N&eacute, el temperature (TN) being 57 K for SNWO and 35 K for SNTO.

By modifying the silicone, a new type of silicone has been obtained which, due to its improved properties, is widely used in many branches of today's industry (cosmetic, pharmaceutical…). By adding different organic groups to polysiloxane molecules, can be achieved higher solvability resistance to solvents and better thermal properties. Oxide nanoparticles, ZnO and TiO2 (more specifically, its crystal modifiers - anatas and rutile), were used to test their size and dispersion in solutions of hydrophilically modified silicones. Acoustic spectroscopy determines the size of oxidative nanoparticles as well as their zeta potential. Total Organic Carbon Analysis (TOC) was used to measure the initial and final (after adsorption) silicone concentration in the solutions. Kinetic measurements have shown that total adsorption on the surface of oxidic nanoparticles occurs within a 5-10 minute time interval. Measurements in a wide range of initial concentrations also determined the types of adsorption isotherms. The results have shown that, depending on the structure of the molecule, the adsorption isotherms of one silicone form Langmuir, and other "high affinity" isotherms.