Effect of preparation methods on microstructures and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

Effect of preparation methods on microstructures and microwave dielectric properties of Ba(Mg_1/3Nb_2/3)O₃ ceramics was investigated. Ba(Mg_1/3Nb_2/3)O₃(BMN) ceramics were prepared by the conventional mixed oxides method and the molten salt synthesis method. It was shown that the single-phase of BMN was obtained at 900 °C in the molten salt synthesis method. No single-phase BMN was obtained in the conventional mixed oxides method, although the calcining temperature was increased up to 1400 °C. BMN powders prepared by the molten salt synthesis method had better sinterability than that prepared by the conventional mixed oxides method. Because of the very different nature of the powders, different microstructures were observed. The molten salt synthesis method ceramics have a higher B-site ordering parameter (S) and larger grain size than that of the conventional mixed oxides ceramics at same sintering temperature. The variation of Qf, ε _r and τ _f were also explained based on the difference in microstructures.     

Formation and properties of ZnO nano-particles from gas phase synthesis processes

ZnO nano-particles have been synthesized in low pressure flow reactors utilizing Zn(CH₃)₂ as precursor. Two different synthesis routes have been employed. A low pressure flame reactor and a microwave reactor were used for synthesis of ZnO particle in Zn(CH₃)₂ doped H₂/O₂/Ar flames and Zn(CH₃)₂ doped Ar/O₂ plasmas, respectively. The particle formation process has been investigated in situ by a particle mass spectrometer. Also, sampled powders have been investigated ex situ by means of FT-IR, XRD, TEM, and UV-VIS. For both synthesis routes nanometer sized ZnO particles were found with particle diameters in the range between 4 to 8 nm. In cases of the flame reactor the results suggest a strong influence of water on the particle formation process.     

The effect of adding nano-SiO2 and nano-Al2O3 on properties of high calcium fly ash geopolymer cured at ambient temperature

This article presents the effect of adding nano-SiO₂ and nano-Al₂O₃ on the properties of high calcium fly ash geopolymer pastes. Nano-particles were added to fly ash at the dosages of 0%, 1%, 2%, and 3% by weight. The sodium hydroxide concentration of 10 molars, sodium silicate to sodium hydroxide weight ratio of 2.0, the alkaline liquid/binder ratio of 0.60 and curing at ambient temperature of 23 °C were used in all mixtures. The results showed that the use of nano-SiO₂ as additive to fly ash results in the decrease of the setting time, while the addition of nano-Al₂O₃ results in only a slight reduction in setting time. Adding 1–2% nano-particles could improve compressive strength, flexural strength, and elastic modulus of pastes due to the formation of additional calcium silicate hydrate (CSH) or calcium aluminosilicate hydrate (CASH) and sodium aluminosilicate hydrate (NASH) or geopolymer gel in geopolymer matrix. In addition, the additions of both nano-SiO₂ and nano-Al₂O₃ enhances the shear bond strength between concrete substrate and geopolymer.     

The influence of γ-Al2O3 and Na2O on the formation of gyrolite in the stirring suspension

Influence of γ-Al₂O₃, Na₂O and hydrothermal synthesis parameters on the gyrolite formation process was established at 200 °C. The molar ratios of primary mixtures were CaO/(SiO₂ + Al₂O₃) = 0.66 and Al₂O₃/(SiO₂ + Al₂O₃) = 0 or 0.025. The amount of NaOH, corresponding to 5% of Na₂O from the mass of dry materials, added in the form of solution. It was determined that in the stirred suspensions under favourable synthesis conditions (active SiO₂ component, dispersive starting materials) gyrolite already forms after 16 h of isothermal curing at 200°C. The stirring affects the sequence of intermediate compounds: gyrolite crystallizes together with Z-phase. γ-Al₂O₃, as the additive in gyrolite synthesis is not usable, because it stimulates other calcium silicate hydrates formation. Na₂O additive positively affects gyrolite synthesis because the duration of gyrolite synthesis shortens almost 2–3 times (6 h, 200°C) to compare with pure mixtures. However, gyrolite is not stable in the mixture with Na₂O and begins to turn into pectolite already after 16 h of isothermal curing. Moreover, the presence of (Na₂O + γ-Al₂O₃) additive stabilizes gyrolite and prevents its transformation to pectolite. Obtained results were confirmed by XRD, DSC and SEM/EDS analysis methods.     

Characterization of ternary (Na0.5K0.5)1?xLixNbO3 lead-free piezoelectric ceramics prepared by molten salt synthesis method

(Na_0.5K_0.5)_1−x Li _x NbO₃ powders and ceramics were prepared by molten salt synthesis method. Pure perovskite-phase powder was obtained at a low temperature of 740 °C with a grain size of below 800 nm. The effects of the LiNbO₃ on phase transition, microstructure, electrical properties, and temperature stability were investigated. A morphotropic phase boundary was identified. The scanning electron microscopy indicated that the (Na_0.5K_0.5)_1−x Li _x NbO₃ powders and ceramics obtained by the molten salt synthesis method have a relatively uniform particle size and microstructure. The results indicate that these materials are promising candidates for lead-free piezoelectric ceramics for practical applications.     

Biological synthesis of calcite crystals using <Emphasis Type="Italic">Scindapsus aureum</Emphasis> petioles

We report a novel strategy for the biological synthesis of calcite crystals using the petioles of the plant Scindapsus aureum. The resultant calcite crystals were characterized by scanning electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffractometry, and electron diffraction. The biomolecules of S. aureum petioles were confirmed by UV–Vis and FT-IR analysis. The results showed that the spherical or rhombohedral calcite crystals were obtained in the cells of S. aureum petioles. Biomimetic synthesis of calcium carbonate (CaCO₃) in aqueous solution containing extracts of S. aureum petioles was also performed to investigate the soluble biomolecules’ influence on crystal growth of CaCO₃. It was found that twinborn spherical calcite crystals were formed, suggesting that the soluble biomolecules of S. aureum play a crucial role in directing the formation of calcite spherical particles. The possible mechanism of formation of CaCO₃ crystals using S. aureum is also discussed; the biomolecules of S. aureum may induce and control the nucleation and growth of CaCO₃ crystals.     

Citrate–nitrate combustion route to the synthesis of (1−<Emphasis Type="Italic">x</Emphasis>)LaCrO<Subscript>3</Subscript>–<Emphasis Type="Italic">x</Emphasis>BiCrO<Subscript>3</Subscript> solid solution

Solid solution of (1−x)LaCrO₃–xBiCrO₃ (x = 0, 0.10, 0.15, 0.20 and 0.25) was prepared via the citrate–nitrate combustion synthesis. Pure perovskite phase was obtained at 800 °C, a much lower synthesis temperature than that needed in the solid-state reactions. The thermodynamics of phase formation and the ceramic sintering mechanism were investigated. The substitution of Bi³⁺ for La³⁺ was found to give a separate exothermic decomposition event in the gels and the precursor did not produce a transient liquid phase while heating to 1200 °C, as was found in ceramics prepared by solid state reaction. This finding shows that the role of Bi₂O₃ in the sintering of the La_1−x Bi _x CrO₃ ceramics depends on the processing method.     

Microwave-assisted route for synthesis of nanosized metal oxides

Microwave-assisted route for the synthesis of nanomaterials has gained importance in the field of synthetic technology because of its faster, cleaner and cost effectiveness than the other conventional and wet chemical methods for the preparation of metal oxide nanoparticles. In the present work, synthesis of metal oxide nanoparticles viz., γ-Fe₂O₃, NiO, ZnO, CuO and Co-γ-Fe₂O₃ were carried out by microwave-assisted route through the thermal decomposition of their respective metal oxalate precursors employing polyvinyl alcohol as a fuel. The metal oxide nanoparticles are then characterized for their size and γ to α (in γ-Fe₂O₃) transition and structure by employing powder X-ray diffraction (XRD) pattern, high-temperature X-ray diffraction (HTXRD) pattern and Fourier transform infrared (FT-IR) spectral studies. The morphology of the samples ranged from nanorods to irregular-shaped particles for different metal oxide samples on the basis of scanning electron microscopy and transmission electron microscopy images. Frequency-dependent dielectric study of the ferrite samples (γ-Fe₂O₃ and Co-Fe₂O₃) showed a similar behaviour, where the dielectric constant decreased rapidly with increase in frequency. Possible explanation for this behaviour is given.     

Microwave-assisted route for synthesis of nanosized metal oxides

Microwave-assisted route for the synthesis of nanomaterials has gained importance in the field of synthetic technology because of its faster, cleaner and cost effectiveness than the other conventional and wet chemical methods for the preparation of metal oxide nanoparticles. In the present work, synthesis of metal oxide nanoparticles viz., γ-Fe₂O₃, NiO, ZnO, CuO and Co-γ-Fe₂O₃ were carried out by microwave-assisted route through the thermal decomposition of their respective metal oxalate precursors employing polyvinyl alcohol as a fuel. The metal oxide nanoparticles are then characterized for their size and γ to α (in γ-Fe₂O₃) transition and structure by employing powder X-ray diffraction (XRD) pattern, high-temperature X-ray diffraction (HTXRD) pattern and Fourier transform infrared (FT-IR) spectral studies. The morphology of the samples ranged from nanorods to irregular-shaped particles for different metal oxide samples on the basis of scanning electron microscopy and transmission electron microscopy images. Frequency-dependent dielectric study of the ferrite samples (γ-Fe₂O₃ and Co-Fe₂O₃) showed a similar behaviour, where the dielectric constant decreased rapidly with increase in frequency. Possible explanation for this behaviour is given.     

Thin Film Synthesis of Ti3SiC2 by Rapid Thermal Processing of Magnetron‐Sputtered Ti?C?Si Multilayer Systems

MAX phase coating could have interesting technical applications in many fields. This paper describes the synthesis of the M_n+1AX_n phase Ti₃SiC₂ by a rapid thermal annealing process of physical vapor deposited Ti? C? Si multilayer thin films on Si (100) and SiO₂ substrates. Annealing temperatures of 800–1000 °C affected the solid state reaction of titanium, carbon and silicon creating titanium‐carbides, ‐silicides, and Ti₃SiC₂. The film structures and chemical compositions were observed by grazing incidence X‐ray diffraction, transmission electron microscopy, and glow discharge optical emission spectroscopy. Analysis after the rapid thermal processing revealed the formation of the polycrystalline M_n+1AX_n phase Ti₃SiC₂ in coexistence with TiSi₂, TiC and Ti₅Si₃, even within a 0 s annealing process. This synthesis method has a high potential for the formation of MAX phases as a high temperature electrical contact material.     

Microstructure and Young’s modulus of high-pressure LixNa1 ? xTayNb1 ? yO3 ceramics

The microstructure and elastic properties of ceramic samples of high-pressure Li _x Na_{1 − x} Ta _y Nb_{1 − y} O₃ perovskite solid solutions have been studied for the first time in relation to their composition and the synthesis temperature. The results demonstrate that, with increasing sintering temperature, the Young’s modulus of the Li_0.17Na_0.83Ta _y Nb_{1 − y} O₃ solid solutions decreases, which can be understood in terms of the recrystallization behavior of the disordered solid solutions under high-pressure synthesis conditions.     

Synthesis Parameters and Their Effects on the Resistivity Anomaly in GdPr1113 Ceramic

Tetragonal Gd_1−x Pr _x BaSrCu₃O_7−δ (GdPr1113) polycrystalline high-temperature superconducting ceramic samples have been synthesized by the standard solid-state reaction process with different calcination and sintering temperatures and characterized by XRD and SEM. The optimum synthesis temperatures for obtaining single phase varied with Pr doping. Higher temperatures were necessary to obtain single phase for x ≥ 0.3. It was found that higher synthesis temperatures improved the electrical characteristics of these materials. The effects of different calcination and sintering temperatures on the anomalous hump in the ρ(T) curves observed at about 80 K is investigated. The percentage of the phase causing the anomaly decreases with the increase of the synthesis temperatures. PACS: 74.72.Bk, 74.62.Bf, 74.25.Fy     

Vacancy ordering and lithium insertion in III2VI3 nanowires

Superlattice structures resulting from vacancy ordering have been observed in many materials. Here we report vacancy ordering behavior in III₂VI₃ nanowires. The formation of layer-like structural vacancies has been achieved during the synthesis of In₂Se₃ nanowires through a vapor-transport route. Doping In₂Se₃ nanowires with small amounts of Ga during synthesis can completely change the structural vacancy ordering from a layer-like to a screw-like pattern for (In _x Ga_1−x )₂Se₃ nanowires. Lithium atoms can fill in the layer-like structural vacancies of In₂Se₃ nanowires and generate new types of vacancy and lithium atom ordering superlattices. The screw-patterned vacancies of (In _x Ga_1−x )₂Se₃ nanowires show reversible lithium insertion. Our results contribute to the understanding of structure property correlations of III₂VI₃ materials used in lithium ion storage, photovoltaics, and phase change memory.     

Simultaneous Synthesis of WO3−x Quantum Dots and Bundle‐Like Nanowires Using a One‐Pot Template‐Free Solvothermal Strategy and Their Versatile Applications

Tungsten oxide (WO_3?x ), a new alternative to conventional semiconductor material, has attracted numerous attentions owning to its widespread potential applications. Various methods have been reported for the synthesis of WO_3?x nanostructures such as nanowires or nanodots. However, templates or surfactants are often required for the synthesis, which significantly complicate the process and hinder the broad applications. Herein, one‐pot template/surfactant‐free solvothermal method is proposed to synthesize the WO_3?x nanostructures including fluorescent quantum dots (QDs) and bundle‐like nanowires simultaneously. The as‐prepared WO_3?x QDs can be well dispersed in aqueous medium, exhibit excellent photoluminescent properties, and show an average size of 3.25 ± 0.25 nm as evidenced by transmission electron microscopy. Meanwhile, the diameter of the WO_3?x nanowires is found to be about 27.5 nm as manifested by the scanning electron microscope images. The generation mechanism for these two WO_3?x nanostructures are systematically studied and proposed. The WO_3?x QDs have been successfully applied in efficient fluorescent staining and specific ferric ion detection. Moreover, the WO_3?x nanowires can be utilized as effective dielectric materials for electromagnetic wave absorption.     

Synthesis and characterization of metal oxide nanorod brushes

Nanorod brushes of α-Al₂O₃, MoO₃ and ZnO have been synthesized using amorphous carbon nanotube (a-CNT) brushes as the starting material. The brushes of α-Al₂O₃ and MoO₃ are made up of single crystalline nanorods. In the case of ZnO brushes, the nanorod bristles are made by the fusion of 15–25 nm size nanoparticles and are porous in nature. Metal oxide nanorod brushes thus obtained have been characterized by XRD, FESEM, TEM and Raman spectroscopy. Single crystalline ruby nanorods were obtained by introducing chromium ions during the synthesis of alumina rods.     

Optimum Synthesis Temperature of (Cu1?xTlx)Ba2Ca3Cu4O12?δ Superconductor

The effect of synthesis temperature on the superconducting properties of (Cu_1−x Tl _x )Ba₂Ca₃Cu₄O_12−δ (CuTl-1234) samples has been explored. Almost all the superconducting parameters studied in this research work are observed to be suppressed with the increase of synthesis temperature beyond 880 °C, which may be due to impurities caused by the volatility of some constituents such as thallium and oxygen deficiencies as well in the final compound. The Fluctuation Induced Conductivity (FIC) analysis has shown a decrease in the cross-over temperature (T ₀) and the shift of three-dimensional (3D) Aslamasov–Larkin (AL) regions to the lower temperature with the increase of synthesis temperature beyond 880 °C. A direct correlation between the cross-over temperature (T ₀), the zero temperature coherence length {ξ _c (0)}, the zero resistivity critical temperature {T _c (R=0)} as well as carrier concentration has also been observed.     

Molybdenum Fixation in Crystalline NZP Matrices

A possibility of fixation of molybdenum present in spent nuclear fuel in ceramic matrices with the structure of the NaZr₂(PO₄)₃ (NZP) type was studied. The crystallochemical features of molybdenum incorporation into various crystallographic NZP structures depending on the synthesis conditions were considered. New molybdate-phosphates of variable composition Na _1-x ZrMo_xO₁₂ (0 x 0.6), crystallizing in the NZP crystal type, were prepared and characterized by X-ray diffraction and IR spectroscopy. The synthesis conditions and the concentration and temperature fields of stability of molybdate-phosphates in the system Na₂O-ZrO₂-MoO₂-P₂O₅ were studied. The crystallographic parameters of single-phase samples were evaluated. The results obtained suggest that the basic factors of formation of chemically stable single-phase NZP ceramics incorporating MoO₄ ^{2 -} anions are the composition of wastes and oxidative synthesis conditions.     

Ionic conductivity of A3 ? 2xNbxAl2 ? x(PO4)3 (A = Li, Na) NASICON-type phosphates

A_{3 − 2x} Nb _x Al_{2 − x} (PO₄)₃ (A = Li, Na) mixed-cation phosphates have been synthesized and characterized by impedance spectroscopy and X-ray diffraction. The synthesis temperature in the lithium system has been optimized. The steric factor is assumed to have a significant effect on the ionic conductivity of these materials.     

Synthesis of Heteropoly Acids and Their Salts Using Mechanochemical Activation

A method is proposed for the synthesis of heteropoly acids from oxides of molybdenum, tungsten, and vanadium via mechanochemical activation. The fundamental principles of this approach to the synthesis of heteropoly acids containing different ligands and heteroatoms are formulated. The new V₂O₅ · nMoO₃ compounds synthesized in this work are found to be highly reactive with phosphoric acid, which is due to the unsaturated coordination of the vanadium cations and the low structural perfection of these compounds. The application area of the proposed method is established. It appears to be most effective in the synthesis of phosphomolybdovanadic and phosphomolybdic heteropoly acids. In some instances, heteropoly acids can be prepared by solid-state reactions, which makes it possible to use V₂O₅ · nMoO₃ compounds with n 6 as starting reagents. The method has a number of important advantages: the process is waste-free, requires a shorter synthesis time and involves a smaller number of steps as compared to the existing processes, affords an increased yield of heteropoly acids, and involves no explosion- or fire-hazardous steps.     

Synthesis of zirconium oxide by hydrolysis of zirconium alkoxide

Submicrometre particles have been prepared from hydrolysis-polycondensation of zirconium alkoxide [Zr(n-C₃H₇O)₄] in ethanolic solution. The properties of these particles (morphology, specific surface area, S _BET, crystal phase and size distribution) after calcination at 450 °C for 5 h were found to depend on the conditions of synthesis, i.e. alkoxide concentration and mole ratio water/alkoxide.