Influence of Grain Size on Dielectric Behavior in Lead-Free 0.5 Ba(Zr0.2Ti0.8)O3-0.5 (Ba0.7Ca0.3)TiO3 Ceramics.

Fine-tuning of grain sizes can significantly influence the interaction between different dielectric phenomena, allowing the development of materials with tailored dielectric resistivity. By virtue of various synthesis mechanisms, a pathway to manipulate grain sizes and, consequently, tune the material's dielectric response is revealed. Understanding these intricate relationships between granulation and dielectric properties can pave the way for designing and optimizing materials for specific applications where tailored dielectric responses are sought. The experimental part involved the fabrication of dense BCT-BZT ceramics with different grain sizes by varying the synthesis (conventional solid-state reaction route and sol-gel) and consolidation methods. Both consolidation methods produced well-crystallized specimens, with Ba0.85Ca0.15O3Ti0.9Zr0.1 (BCTZ) perovskite as the major phase. Conventional sintering resulted in microstructured and submicron-structured BCT-BZT ceramics, with average grain sizes of 2.35 µm for the solid-state sample and 0.91 µm for the sol-gel synthesized ceramic. However, spark plasma sintering produced a nanocrystalline specimen with an average grain size of 67.5 nm. As the grain size decreases, there is a noticeable decrease in the maximum permittivity, a significant reduction in dielectric losses, and a shifting of the Curie temperature towards lower values.

High-Entropy Lead-Free Perovskite Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 Powders and Related Ceramics: Synthesis, Processing, and Electrical Properties.

A novel high-entropy perovskite powder with the composition Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 was successfully synthesized using a modified Pechini method. The precursor powder underwent characterization through Fourier Transform Infrared Spectroscopy and thermal analysis. The resultant Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 powder, obtained post-calcination at 900 °C, was further examined using a variety of techniques including X-ray diffraction, Raman spectroscopy, X-ray fluorescence, scanning electron microscopy, and transmission electron microscopy. Ceramic samples were fabricated by conventional sintering at various temperatures (900, 950, and 1000 °C). The structure, microstructure, and dielectric properties of these ceramics were subsequently analyzed and discussed. The ceramics exhibited a two-phase composition comprising cubic and tetragonal perovskites. The grain size was observed to increase from 35 to 50 nm, contingent on the sintering temperature. All ceramic samples demonstrated relaxor behavior with a dielectric maximum that became more flattened and shifted towards lower temperatures as the grain size decreased.

Comparative Study of MgO Nanopowders Prepared by Different Chemical Methods.

Magnesium oxide (MgO) was synthesized by three different methods: the sol-gel (SG), microwave-assisted sol-gel (MW), and hydrothermal (HT) methods for comparing the influence of the preparation conditions on the properties of the products. The powders were annealed at 450 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM/HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), BET specific surface area and porosity, photoluminescence, and UV-Vis spectroscopy. The samples consisted mainly of periclase as a crystalline phase, and the MW and HT preparation methods generated particles with higher specific surface areas. The powders had less-defined morphologies and high levels of aggregation. The optical band gaps of the samples were determined from UV DRS, and the photocatalytic activities of the magnesium oxides obtained by the three methods towards the degradation of methyl orange (MO) under UV light irradiation was evaluated.

Deciphering the role of water and a zinc-doping process in a polyol-based approach for obtaining Zn/Co/Al-based spinels: toward "green" mesoporous inorganic pigments.

Two new families of zinc/cobalt/aluminum-based pigments, with a unique composition, were obtained through the polyol method. The hydrolysis process of a mixture of Co(CH3COO)2, Zn(acac)2 and Al(acac)3 (acac- = acetylacetonate ion) in 1,4-butanediol afforded dark blue gels (wPZnxCo1-xAl), in the presence of a supplementary amount of water, and light green powders (PZnxCo1-xAl), respectively, for the water-free procedure (x = 0, 0.2, 0.4). The calcination of the precursors yielded dark green (wZnxCo1-xAl) and blue (ZnxCo1-xAl) products. XRD measurements and Rietveld refinement indicate the co-existence of three spinel phases, in different proportions: ZnxCo1-xAl2O4, Co3O4 and the defect spinel, γ-Al2.67O4. The Raman scattering and XPS spectra are in agreement with the compositions of the samples. The morphology of wZnxCo1-xAl consists of large and irregular spherical particle aggregates (ca. 5-100 mm). Smaller agglomerates (ca. 1-5 mm) with a unique silkworm cocoon-like hierarchical morphology composed of cobalt aluminate cores covered with flake-like alumina shells are formed for ZnxCo1-xAl. TEM and HR-TEM analyses revealed the formation of crystalline, polyhedral particles of 7-43 nm sizes for wZnxCo1-xAl, while for ZnxCo1-xAl, a duplex-type morphology, with small (7-13 nm) and larger (30-40 nm) particles, was found. BET assessment showed that both series of oxides are mesoporous materials, with different pore structures, with the water-free samples exhibiting the largest surface areas due, most likely, to the high percent of aluminum oxide. A chemical mechanism is proposed to highlight the role of the water amount and the nature of the starting compounds in the hydrolysis reaction products and, further, in the morpho-structural features and composition of the resulting spinel oxides. The CIE L*a*b* and C* colorimetric parameters indicate that the pigments are bright, with a moderate degree of luminosity, presenting an outstanding high blueness.

Copper-/Zinc-Doped TiO2 Nanopowders Synthesized by Microwave-Assisted Sol-Gel Method.

Using the microwave-assisted sol-gel method, Zn- and Cu-doped TiO2 nanoparticles with an anatase crystalline structure were prepared. Titanium (IV) butoxide was used as a TiO2 precursor, with parental alcohol as a solvent and ammonia water as a catalyst. Based on the TG/DTA results, the powders were thermally treated at 500 °C. XRD and XRF revealed the presence of a single-phase anatase and dopants in the thermally treated nanoparticles. The surface of the nanoparticles and the oxidation states of the elements were studied using XPS, which confirmed the presence of Ti, O, Zn, and Cu. The photocatalytic activity of the doped TiO2 nanopowders was tested for the degradation of methyl-orange (MO) dye. The results indicate that Cu doping increases the photoactivity of TiO2 in the visible-light range by narrowing the band-gap energy.

Nanoscale Control of Structure and Composition for Nanocrystalline Fe Thin Films Grown by Oblique Angle RF Sputtering.

The use of Fe films as multi-element targets in space radiation experiments with high-intensity ultrashort laser pulses requires a surface structure that can enhance the laser energy absorption on target, as well as a low concentration and uniform distribution of light element contaminants within the films. In this paper, (110) preferred orientation nanocrystalline Fe thin films with controlled morphology and composition were grown on (100)-oriented Si substrates by oblique angle RF magnetron sputtering, at room temperature. The evolution of films key-parameters, crucial for space-like radiation experiments with organic material, such as nanostructure, morphology, topography, and elemental composition with varying RF source power, deposition pressure, and target to substrate distance is thoroughly discussed. A selection of complementary techniques was used in order to better understand this interdependence, namely X-ray Diffraction, Atomic Force Microscopy, Scanning and Transmission Electron Microscopy, Energy Dispersive X-ray Spectroscopy and Non-Rutherford Backscattering Spectroscopy. The films featured a nanocrystalline, tilted nanocolumn structure, with crystallite size in the (110)-growth direction in the 15-25 nm range, average island size in the 20-50 nm range, and the degree of polycrystallinity determined mainly by the shortest target-to-substrate distance (10 cm) and highest deposition pressure (10-2 mbar Ar). Oxygen concentration (as impurity) into the bulk of the films as low as 1 at. %, with uniform depth distribution, was achieved for the lowest deposition pressures of (1-3) × 10-3 mbar Ar, combined with highest used values for the RF source power of 125-150 W. The results show that the growth process of the Fe thin film is strongly dependent mainly on the deposition pressure, with the film morphology influenced by nucleation and growth kinetics. Due to better control of film topography and uniform distribution of oxygen, such films can be successfully used as free-standing targets for high repetition rate experiments with high power lasers to produce Fe ion beams with a broad energy spectrum.

CuBi2O4 Synthesis, Characterization, and Application in Sensitive Amperometric/Voltammetric Detection of Amoxicillin in Aqueous Solutions.

CuBi2O4 synthesized by thermolysis of a new Bi(III)-Cu(II) oxalate coordination compound, namely Bi2Cu(C2O4)4·0.25H2O, was tested through its integration within carbon nanofiber paste electrode, namely CuBi/carbon nanofiber (CNF), for the electrochemical detection of amoxicillin (AMX) in the aqueous solution. Thermal analysis and IR spectroscopy were used to characterize a CuBi2O4 precursor to optimize the synthesis conditions. The copper bismuth oxide obtained after a heating treatment of the precursor at 700 °C/1 h was investigated by an X-ray diffraction and scanning electron microscopy. The electrochemical behavior of CuBi/CNF in comparison with CNF paste electrode showed the electrocatalytic activity of CuBi2O4 toward amoxicillin detection. Two potential detections, with one at the potential value of +0.540 V/saturated calomel electrode (SCE) and the other at the potential value of -1.000 V/SCE, were identified by cyclic voltammetry, which were exploited to develop the enhanced voltammetric and/or amperometric detection protocols. Better electroanalytical performance for AMX detection was achieved for CuBi/CNF using differential-pulsed and square-wave voltammetries than others reported in the literature. Very nice results obtained through anodic and cathodic currents recorded at +0.750 V/SCE and -1.000 V/SCE in the same time period using a pseudo multiple-pulsed amperometry technique showed the great potential of the CuBi/CNF paste electrode for practical applications in amoxicillin detection in aqueous solutions.

Lanthanum Ferrite Ceramic Powders: Synthesis, Characterization and Electrochemical Detection Application.

The perovskite-type lanthanum ferrite, LaFeO3, has been prepared by thermal decomposition of in situ obtained lanthanum ferrioxalate compound precursor, LaFe(C2O4)3·3H2O. The oxalate precursor was synthesized through the redox reaction between 1,2-ethanediol and nitrate ion and characterized by chemical analysis, infrared spectroscopy, and thermal analysis. LaFeO3 obtained after the calcination of the precursor for at least 550-800 °C/1 h have been investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). A boron-doped diamond electrode (BDD) modified with LaFeO3 ceramic powders at 550 °C (LaFeO3/BDD) by simple immersion was characterized by cyclic voltammetry and tested for the voltammetric and amperometric detection of capecitabine (CCB), which is a cytostatic drug considered as an emerging pollutant in water. The modified electrode exhibited a complex electrochemical behaviour by several redox systems in direct relation to the electrode potential range. The results obtained by cyclic voltammetry (CV), differential-pulsed voltammetry (DPV), and multiple-pulsed amperometry proved the electrocatalytic effect to capecitabine oxidation and reduction and allowed its electrochemical detection in alkaline aqueous solution.

Influence of Sintering Strategy on the Characteristics of Sol-Gel Ba1-xCexTi1-x/4O3 Ceramics.

Single-phase Ce3+-doped BaTiO3 powders described by the nominal formula Ba1-xCexTi1-x/4O3 with x = 0.005 and 0.05 were synthesized by the acetate variant of the sol-gel method. The structural parameters, particle size, and morphology are strongly dependent on the Ce3+ content. From these powders, dense ceramics were prepared by conventional sintering at 1300 °C for 2 h, as well as by spark plasma sintering at 1050 °C for 2 min. For the conventionally sintered ceramics, the XRD data and the dielectric and hysteresis measurements reveal that at room temperature, the specimen with low cerium content (x = 0.005) was in the ferroelectric state, while the samples with significantly higher Ce3+ concentration (x = 0.05) were found to be in the proximity of the ferroelectric-paraelectric phase transition. The sample with low solute content after spark plasma sintering exhibited insulating behavior, with significantly higher values of relative permittivity and dielectric losses over the entire investigated temperature range relative to the conventionally sintered sample of similar composition. The spark-plasma-sintered Ce-BaTiO3 specimen with high solute content (x = 0.05) showed a fine-grained microstructure and an almost temperature-independent colossal dielectric constant which originated from very high interfacial polarization.

Bi1-xEuxFeO3 Powders: Synthesis, Characterization, Magnetic and Photoluminescence Properties.

Europium substituted bismuth ferrite powders were synthesized by the sol-gel technique. The precursor xerogel was characterized by thermal analysis. Bi1-xEuxFeO3 (x = 0-0.20) powders obtained after thermal treatment of the xerogel at 600 °C for 30 min were investigated by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectroscopy, and Mössbauer spectroscopy. Magnetic behavior at room temperature was tested using vibrating sample magnetometry. The comparative results showed that europium has a beneficial effect on the stabilization of the perovskite structure and induced a weak ferromagnetism. The particle size decreases after the introduction of Eu3+ from 167 nm for x = 0 to 51 nm for x = 0.20. Photoluminescence spectroscopy showed the enhancement of the characteristic emission peaks intensity with the increase of Eu3+ concentration.

Facile, high yield ultrasound mediated protocol for ZnO hierarchical structures synthesis: Formation mechanism, optical and photocatalytic properties.

Hierarchical flowers-like zinc oxide structures have been successfully obtained by a simple and fast ultrasound-assisted method performed in a ordinary ultrasonic bath using an ammonia solution and zinc acetate, in the absence of any surfactant or template. The composition, structure, crystallinity, morphology and optical properties of the materials obtained at different ultrasound irradiation times were characterized by infrared, UV-Vis and photoluminescence spectroscopy, X-ray diffraction, scanning and transmission electron microscopy investigations. It was proved that the ultrasound irradiation time manipulates both the defect content (implicit the photoluminescent properties) and morphology of the ZnO materials: shorter irradiation times leads to the synthesis of high-defected ZnO structures of flower morphology with triangular-shaped petals, while higher irradiation times favours the formation of low-defected ZnO structures with tipped rod-like petals. A plausible growth mechanism of the architectures that implies aggregation via oriented attachment followed by an Ostwald ripening is advanced based on these results. The ZnO flower-like structures present high photocatalytic activities, a total phenol mineralization being registered in the case of visible light experiments. Electron-spin resonance measurements demonstrate the generation of reactive oxygen species, namely hydroxyl radicals but also C centred radicals adducts derived most probable from the residual acetate adsorbed on ZnO surface.

A general, eco-friendly synthesis procedure of self-assembled ZnO-based materials with multifunctional properties.

A bioinspired one-pot approach for the synthesis of ZnO-carbohydrate hierarchical architectures was developed. The synergy between a saccharide (mono-, di- or polysaccharide) that contains d-glucose units and triethanolamine is the key parameter of the synthetic methodology. The morphology of the ZnO composites is dictated by the saccharide used, and rod, spindle, solid and hollow spherical-like ZnO structures are obtained by varying the carbohydrate. The synthesized composites present good photocatalytic and antimicrobial activity.

Biopolymer starch mediated synthetic route of multi-spheres and donut ZnO structures.

A starch-assisted synthetic methodology of multispheres ZnO-starch biocomposites was developed. An additional thermal processing of the ZnO-starch composites induces the formation of ZnO with donut-like morphology. The synthesis of single-phase zinc oxide with a spherical morphology is conditioned by the presence of starch, which acts as template, stabilizing/capping agent. The synthesized structures present significant photocatalytic activities; a total phenol mineralization is attained with the donut-like ZnO photocatalyst under visible light irradiation, due to a cumulative effect of the its relatively large specific surface area, high crystallinity and favorable combination of defects for band narrowing, which together permit an enhanced utilization rate of the light.

Differentiation of mesenchymal stem cells onto highly adherent radio frequency-sputtered carbonated hydroxylapatite thin films.

In this work, an improved version of the radio frequency magnetron sputtering (RF-MS) technique was used to prepare highly adherent B-type carbonated hydroxylapatite (B-CHA) thin films. Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction studies proved that the coatings maintained the composition and revealed the polycrystalline structure of HA. Scanning electron microscopy analysis showed that the CHA films are rough and exhibit a homogeneous microstructure. Energy-dispersive X-ray spectroscopy (EDX) mapping demonstrated a uniform distribution of the Ca and P cations while a Ca/P ratio of 1.8 was found. In addition, the FTIR experiments showed a remarkable reproducibility of the nanostructures. Human mesenchymal stem cells (hMSCs), in vitro differentiated osteoblasts, and explanted bone cells were grown over the surface of CHA coatings for periods between a few hours and 21 days. Osteoprogenitor cells maintained viability and characteristic morphology after adhesion on CHA coatings. Ki67-positive osteoblasts were the evidence of cell proliferation events. Cells showed positive staining for markers of osteoblast phenotype such as collagen type I, bone sialoprotein and osteonectin. Our data showed the formation of mineralized foci by differentiation of hMSCs to human primary osteoblasts after cultivation in osteogenic media on RF-sputtered films. The results demonstrate the capacity of B-type CHA coating to support MSCs adhesion and osteogenic differentiation ability.