Different Amounts Of Dopant Research Articles

Transition metal (Nb and W) doped TiO2 nanostructures: The role of metal doping in their photocatalytic activity and ozone gas-sensing performance

Semiconducting metal oxide nanostructures have drawn much attention from the researchers due to several advantages related to their wide-ranging applications, such as photocatalytic activity and gas-sensing performance. In this way, the effect of metal ions on the structural, morphological and electronic properties of the as-prepared samples were investigated by X-ray diffraction (XRD), Raman spectroscopy, UV–visible diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS) and electron microscopy techniques. XRD analysis confirmed that all MxTi1−xO2 (M = Nb and W) samples presented only the TiO2 anatase phase despite the different amounts of dopant. Additionally, scanning electron microscopy (SEM) showed that the increased metal ion content leads to a morphological evolution from anisotropic to isotropic nanostructures, which consequently reduces their size. It was observed that the presence of W and Nb as dopants clearly induces a change in the surface characteristics of the nanostructures, favoring the photodegradation of cationic dyes, which does not occur for Rhodamine (RhB) since the photocatalytic mechanism appears strictly related to carrier charges. From the studied samples, W0.29Ti0.71O2 presented interesting ozone (O3) gas-sensing performance, which was evidenced by their working temperature (below 150 °C), sensor response, stability and good range of detection.

Monatomic phase change memory.

Phase change memory has been developed into a mature technology capable of storing information in a fast and non-volatile way1-3, with potential for neuromorphic computing applications4-6. However, its future impact in electronics depends crucially on how the materials at the core of this technology adapt to the requirements arising from continued scaling towards higher device densities. A common strategy to fine-tune the properties of phase change memory materials, reaching reasonable thermal stability in optical data storage, relies on mixing precise amounts of different dopants, resulting often in quaternary or even more complicated compounds6-8. Here we show how the simplest material imaginable, a single element (in this case, antimony), can become a valid alternative when confined in extremely small volumes. This compositional simplification eliminates problems related to unwanted deviations from the optimized stoichiometry in the switching volume, which become increasingly pressing when devices are aggressively miniaturized9,10. Removing compositional optimization issues may allow one to capitalize on nanosize effects in information storage.

Influence of rare-earth metal on the zinc oxide nanostructures: application in the photocatalytic degradation of methylene blue and p-nitro phenol

Abstract Rare-earth cerium (Ce)-doped zinc oxide (ZnO) spherical nanoparticles were synthesized by using the co-precipitation method. The doped materials were characterized by means of the X-ray diffraction, Williamson-Hall Plot, and field emission scanning electron microscopy analyses. The prepared nanoparticles exhibit a hexagonal wurtzite structure as observed from the XRD measurements. Energy dispersive X-ray spectroscopy data confirmed the purity of the prepared samples. The photocatalytic activity of the rare-earth Ce-doped ZnO spherical nanoparticles was investigated through the degradation of methylene blue (MB) and p-nitrophenol (PNP) solution under UV light radiation. Among the different amounts of dopant, 5 mole% Ce-doped ZnO nanoparticles showed the highest degradation with UV light radiation for both MB dye and PNP solution. The particle size, morphology, and separation of the photo-induced electron–hole pair are the main factors that influence photocatalytic activity. The probable mechanisms of photocatalytic degradation and mineralization of MB and PNP are also explained by liquid chromatography–mass spectrometry analysis.

Nonagglomerated Iron Oxyhydroxide Akaganeite Nanocrystals Incorporating Extraordinary High Amounts of Different Dopants

Dispersible nonagglomerated akaganeite (β-FeOOH) nanocrystals doped with various elements in different oxidation states such as Co(II), Ni(II), V(III), Ti(IV), Sn(IV), Si(IV), and Nb(V) were prepared using a microwave-assisted solvothermal synthesis in tert-butanol. The doping elements could be incorporated in very high concentrations of up to 20 at. %, which is attributed to the kinetic control of the phase formation during the solvothermal reaction, together with the extremely small crystal size, which can stabilize the unusual structural compositions. The particle morphology is mostly anisotropic consisting of nanorods ∼4 nm in width and varying length. Depending on the doping element, the length ranges from ∼4 nm, resulting in an almost-spherical shape, to 90 nm, giving the highest aspect ratio. The particles are perfectly dispersible in water, giving stable colloidal dispersions that can be deposited on different substrates to produce thin films 35–250 nm thick. In addition, films up to 30 μm thick, ...

Synthesis of Mo-doped CeO2 by the Combustion Method for Carbon-Air Fuel Cells Applications: Study of Composition, Crystalline Structure and Mechanical Properties

Molybdenum-doped ceria (CMO) is a promising material for the fabrication of anodes for carbon-air fuel cells. In this work, Ce0.9Mo0.1O2+ δ was synthesized by the combustion method, which reports lower synthesis times than the solid-state reaction and Pechini’s methods. The material obtained does not present impurities (determined by EDS analysis) and forms Fm-3m (225 space group) single phase fluorite-type structures with a cell parameter of ca. 5.419 Å (determined by Rietveld refinement). The mechanical properties of this material were studied using dense pellets produced by pressing the powders (pressure of ca. 105 MPa) and sintering the tablets obtained at 1000°C for 24 hours. The Young’s modulus (291.7 GPa) and Vickers microhardness (between 4694 and 2474.4 MPa) were determined by using the resonant frequency method and Struers microhardness tester, respectively. Future work considers the complete characterization of mechanical and electrical properties of CMO with different amounts of dopant.

Improved Li-ion conductivity of 0.7Li4SiO4–0.3Li3PO4 by aluminum doping

The solid solution 0.7Li4SiO4–0.3Li3PO4 (LSP) is known to be a Li-ion conducting ceramic. Aluminum doping of it was carried out to increase the ionic conductivity. The aluminum-doped LSP (LASP) was prepared with different amounts of dopant, to examine the effect of the amount of dopant on the ionic conductivity. LASP was synthesized using a sol-gel reaction and subsequent calcination. The crystalline phase of the LASP was analyzed by powder X-ray diffraction (PXRD) and identified as the monoclinic phase of 0.7Li4−yAlySiO4–0.3Li3PO4. However, addition of aluminum results in the precipitation of a secondary crystalline Li2SiO3 phase. Li-ion conductivity was estimated by using electrochemical impedance spectroscopic (EIS) analysis on an LASP pellet that had been sintered at 1000°C. In spite of the precipitation of the Li2SiO3 phase, Li-ion conductivity was increased by aluminum doping at 150°C to approximately 20 times that of the undoped material (LSP), which effect is considered to be associated with vacancies generated by the aluminum doping providing conducting paths for the Li-ion.

Sonochemical Synthesis, Characterization and Sonocatalytic Performance of Terbium-Doped CdS Nanoparticles

Terbium-doped cadmium sulfide nanoparticles with different terbium contents were successfully synthesized via sonochemical route. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, photoelectron X-ray spectroscopy, and UV–Vis diffuse reflectance spectroscopy techniques. The as-prepared nanocatalyst were used for sonocatalytic degradation of Methylene Blue. Among the different amounts of dopant, 8 % Tb-doped CdS showed the highest sonocatalytic activity. The order of inhibitory effect of radical scavengers was 1, 4 Benzoquinone > SO3 2− > CO2 3−> I−. The effects of various parameters such as initial dye concentration, catalyst loading, ultrasonic power, and the presence of radical scavengers were investigated.

La-doped ZnO nanoflower as photocatalyst for methylene blue dye degradation under UV irradiation

Lanthanum doped ZnO flower-like structured nanoparticles were synthesized through microwave assisted sol–gel technique. X-ray diffraction, scanning electron microscopy, transmission electron microscopy analysis confirmed the size, structural morphology and successful compound formation of the samples. The band gap was calculated from Tauc’s plot using UV–Vis spectroscopy data. Lanthanum doped ZnO nanoparticles were used for the photocatalytic degradation of methylene blue dye under UV light irradiation. Compared to pure ZnO sample, La-doped samples exhibited higher photocatalytic dye degradation under UV light irradiation with short time duration. Among the different amounts of dopant, 3 mol% La-doped ZnO nano rods showed the highest degradation with short time UV light irradiation (60 min). Other factors such as particle size, morphology and defects also affect the photocatalytic activity. In our study, the main factor that influence photocatalytic activity is the separation of photo induced electron–hole pair due to defects formation in the sample. The 3 mol% sample has the appropriate electron–hole separation due to defects compared to pure ZnO. The influence of defects on the photocatalytic activity of all samples has been revealed using photoluminescence spectroscopy analysis. Furthermore, the effect of various operational parameters such as photocatalyst quantity, dye concentration and dopant concentrations were also optimized.

Custom-Designed Nanomaterial Libraries for Testing Metal Oxide Toxicity

Advances in aerosol technology over the past 10 years have enabled the generation and design of ultrafine nanoscale materials for many applications. A key new method is flame spray pyrolysis (FSP), which produces particles by pyrolyzing a precursor solution in the gas phase. FSP is a highly versatile technique for fast, single-step, scalable synthesis of nanoscale materials. New innovations in particle synthesis using FSP technology, including variations in precursor chemistry, have enabled flexible, dry synthesis of loosely agglomerated, highly crystalline ultrafine powders (porosity ≥ 90%) of binary, ternary, and mixed-binary-and-ternary oxides. FSP can fulfill much of the increasing demand, especially in biological applications, for particles with specific material composition, high purity, and high crystallinity. In this Account, we describe a strategy for creating nanoparticle libraries (pure or Fedoped ZnO or TiO₂) utilizing FSP and using these libraries to test hypotheses related to the particles' toxicity. Our innovation lies in the overall integration of the knowledge we have developed in the last 5 years in (1) synthesizing nanomaterials to address specific hypotheses, (2) demonstrating the electronic properties that cause the material toxicity, (3) understanding the reaction mechanisms causing the toxicity, and (4) extracting from in vitro testing and in vivo testing in terrestrial and marine organisms the essential properties of safe nanomaterials. On the basis of this acquired knowledge, we further describe how the dissolved metal ion from these materials (Zn²⁺ in this Account) can effectively bind with different cell constituents, causing toxicity. We use Fe-S protein clusters as an example of the complex chemical reactions taking place after free metal ions migrate into the cells. As a second example, TiO₂ is an active material in the UV range that exhibits photocatalytic behavior. The induction of electron-hole (e⁻/h⁺) pairs followed by free radical production is a key mechanism for biological injury. We show that decreasing the bandgap energy increases the phototoxicity in the presence of near-visible light. We present in detail the mechanism of electron transfer in biotic and abiotic systems during light exposure. Through this example we show that FSP is a versatile technique for efficiently designing a homologous library, meaning a library based on a parent oxide doped with different amounts of dopant, and investigating the properties of the resulting compounds. Finally, we describe the future outlook and state-of-the-art of an innovative two-flame system. A double-flame reactor enables independent control over each flame, the nozzle distances and the flame angles for efficient mixing of the particle streams. In addition, it allows for different flame compositions, flame sizes, and multicomponent mixing (a grain-grain heterojunction) during the reaction process.

Effect of Low Concentration Sn Doping on Optical Properties of CdS Films Grown by CBD Technique

Thin and transparent films of doped cadmium sulfide (CdS) were obtained on commercial glass substrates by Chemical Bath Deposition (CBD) technique. The films were doped with low concentration of Sn, and annealed in air at 300 °C for 45 min. The morphological characterization of the films with different amounts of dopant was made using SEM and EDAX analysis. Optical properties of the films were evaluated by measuring transmittance using the UV-vis spectrophotometer. A comparison of the results revealed that lower concentration of Sn doping improves transmittance of CdS films and makes them suitable for application as window layer of CdTe/CIGS solar cells.

Microwave absorption properties of Mn- and Ni-doped zinc oxides

Microwave absorption properties of Mn- and Ni-doped zinc oxides were assessed in this study. Samples were prepared by the decomposition of acetate solid solutions. By changing the concentration of dopant ions in the reaction solutions, zinc oxides with different amounts of dopant were obtained. The morphologies, chemical compositions, and structures of the samples were investigated by scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray powder diffraction. Electromagnetic characteristics of the doped samples were assessed by vector network analysis at a frequency range of 2–16 GHz. Both the real and imaginary parts of the complex permittivity decreased as Mn or Ni concentration increased. Results indicate that, compared with pure ZnO, Mn- and Ni-doped zinc oxides exhibit excellent microwave absorption properties. The highest level of microwave absorption observed was 80.7 dB at a frequency of 9.8 GHz, and the best frequency bandwidth was 8.6 GHz at reflection loss values below −10 dB.

Caracterização morfológica e luminescente de nanopartículas de aluminato de zinco dopadas com Eu3+

Este trabalho reporta a obtenção de nanopartículas de aluminato de zinco dopado com Eu3+, por meio do método de síntese por reação de combustão. Foram preparadas quatro amostras com diferentes concentrações de dopante, para avaliar o efeito do teor de Eu3+ na luminescência dos pós obtidos. Os resultados de difração de raios X confirmaram a formação da fase espinélio ZnAl2O4 e também traços de fases secundárias identificadas como EuAlO3 e ZnO, em quantidade diretamente proporcional ao teor de dopante das amostras. O espectro de emissão foi excitado em 265 nm (lambdamax), o qual apresentou picos característicos do íon Eu3+ localizados em torno de 578, 591 613, 653 e 703 nm. Os resultados obtidos por microscopia eletrônica de varredura apresentam aglomerados em forma de placas irregulares formadas por nanopartículas com pontos dispersos de fase secundaria na superfície. Baseado nos resultados verificou-se a dependência da intensidade de luminescência com o teor e também com a forma de incorporação do íon Eu3+, inserido na rede hospedeira, adsorvido na superfície de nanopartículas ou formando uma segunda fase.

Improvements in the figure of merit for tunable microwave dielectrics using combinatorial approach

Ferroelectric/dielectric materials are useful for a variety of different applications. Addition of small amounts of different dopants often dramatically improves the materials performance. The conventional approach to exploring new materials is to make and characterize samples of discrete composition one at a time. In an effort to accelerate this process, we fabricate a combinatorial materials chips containing 256 differently doped (Ba, Sr)TiO3 thin films. From this study, we found that tungsten doping in this class of materials greatly reduces the dielectric loss and does not significantly affect the tunability of these materials. As the result, the overall figures of merit of the materials are greatly improved.

Crystallographic Orientation Relationships between the Primary and Secondary Recrystallized Grains in Multi-Layer Molybdenum Crystals.

A large-scale and multi-layer crystal was prepared from hot-rolled multi-laminated molybdenum sheet doped and stacked alternately with different amounts of dopant by means of secondary recrystallization. It was found that the potential nucleus of the secondary grain from layers with different amounts of dopant occurred first at layer with a small amount of dopant and then grew into the layer with a large amount of dopant during a higher temperature annealing. The orientation of secondary grain developed from each layer was also closely related to the texture gradients in the thickness direction for primary recrystallized sheet. Most of the orientation of multi-layer crystal sheet corresponded to very weak components in the primary recrystallization textures and were related by a rotation of approximately 15°C-30°C about and axes relative to the strong primary {001} and {111} components. Consequently, the main orientations of the secondary grains developed from quintuple-layer molybdenum crystal are composed of a near {100} for the surface layer, a near {112} for the central layer and a near {113} +{112} for the layer between surface and central ones.

The motion of ions in potassium-doped polyacetylene

Abstract When the computer-simulated potassium-doped polyaceteylene lattice is relaxed free of restrictions, the chains of the host polymer deviate from strict planarity. On introducing a K+ vacancy in two lattices containing different amounts of dopant, defective lattice calculations show that the structure with the lower doping level is favoured, but that samples probably also contain regions with the higher doping level. The mobility of the K+ ions is expected to be very high when vacancies are present in the dopant sublattice.