Preparation and characterization of BaSnO<Subscript>3</Subscript> powders by hydrothermal synthesis from tin oxide hydrate gel

BaSnO₃ powders have been prepared from the tin oxide hydrate gel and the Ba(OH)₂ solution via hydrothermal synthesis route. The influence of the process parameters on the characteristics of BaSnO₃ has been studied. A powder with the single-phase of BaSnO₃ can be obtained only when the concentration of Ba(OH)₂ solution is no less than 0.2 M and the ratio of Ba:Sn lies between 1.0 and 1.2. At a hydrothermal temperature of 330 °C or higher, uniform BaSnO₃ powders can be directly prepared through hydrothermal reaction. When the hydrothermal temperature is lower than 250 °C, the as-prepared powder consists of BaSn(OH)₆ that transforms through an amorphous phase into BaSnO₃ by calcination at 260 °C. In the hydrothermal temperature range of 130–250 °C, a higher temperature can promote the crystallization of BaSnO₃, increases its specific surface area and decreases the average particle size. The duration of the hydrothermal reaction affects the morphology of the powder particles. The effects of the nonaqueous solvents on the properties of powders have also been investigated.     

Ultrafine Cr-Doped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Prepared by Detonation Synthesis

Data are presented on the phase composition, particle size distribution, EPR, and luminescence of ultrafine chromium-doped alumina powders prepared by detonation synthesis. The largest particles in the powders are shown to consist mainly of a Cr₂O₃ solid solution in α-Al₂O₃. The luminescence spectrum of fine particles shows, in addition to lines characteristic of ruby, extra lines which are tentatively attributed to Cr³⁺ ions incorporated substitutionally into θ-Al₂O₃.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 948–954.Original Russian Text Copyright © 2005 by Lyamkina, Chiganova, Slabko, Vorotynov, Taranova.     

Synthesis and microstructure of nanocrystalline Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> powders

Nanocrystalline ytterbia powders have been synthesized using different precursors prepared by precipitation from nitrate solutions: ytterbium carbonates, oxalates, and hydroxides. The powders have been characterized by X-ray diffraction and scanning electron microscopy. The nature of the precursor has no effect on the crystallization temperature of ytterbia but influences its microstructure. The particles range in shape from spherical to platelike. The average crystallite size of the Yb₂O₃ powders is 20–25 nm. Raising the heat-treatment temperature from 600 to 1000°C increases the crystallite size to 33–46 nm. The highest thermal stability is offered by the ytterbia powders prepared through carbonate decomposition.     

Synthesis and characterization of nanoboron powders prepared with mechanochemical reaction between B<Subscript>2</Subscript>O<Subscript>3</Subscript> and Mg powders

Amorphous boron powders with small particle size, narrow size distribution and high purity are very important in the high-tech fields. Mechanochemical synthesis was used to prepare amorphous boron nanoparticles. Synthesis process stage was carried out using stoichiometric amounts of B₂O₃ and Mg powders (6.7 g). Milling was carried out under argon atmosphere in the high-energy planetary ball mill with a ball-to-powder weight ratio (32 : 1) for 10 h. The vial rotation speed was about 440 rpm. Milled products were leached by 28% hydrochloric acid (only one) to remove impurities. Boron powders were obtained after centrifuging, decanting, washing and drying operations. Sample was characterized by inductively coupled plasma (ICP), energy-dispersive spectroscopy, X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ICP results showed that boron powders with purity about 91 wt% can be prepared in the planetary ball mill. Also, the leached powders had an amorphous structure. According to the SEM observation, average particle size of boron powders was smaller than 32 nm and the yield of synthesized nanoboron was more than 74%.     

Microwave-hydrothermal synthesis of Y<Subscript>3</Subscript>Fe<Subscript>3.35</Subscript>Al<Subscript>1.65</Subscript>O<Subscript>12</Subscript> nanoparticles for magneto-hyperthermia application

Crystalline aluminum substituted yttrium iron garnet nanoparticles Y₃Fe_3.35Al_1.65O₁₂ (YIG) was synthesized by hydrothermal microwave synthesis at 140 °C with soaking times ranging from 15 to 60 min. X-ray diffraction confirmed the single-phase YIG nanoparticles excluding the presence of any other phases in the reaction products. The Raman spectra revealed that the largest soaking time provides greater energy crystallization causing changes of lattice vibration and a certain degree of disorder in the crystal lattice. Field emission gun-scanning electron microscopy and high resolution transmission electronic microscopic revealed a homogeneous size distribution of nanometric YIG powders with agglomerated particles. Magnetic measurements were achieved by using a vibrating-sample magnetometer unit. YIG nanoparticles have great potential in magneto-hyperthermia application once in vivo applications magnetic induction heating ferromagnetic compounds generate heat in AC magnetic fields.     

Synthesis of the Ti<Subscript>2</Subscript>AlC MAX Phase with a Reduction Step via Combustion of a TiO<Subscript>2</Subscript> + Mg + Al + C Mixture

Technologically viable principles have been developed for the preparation of the MAX phase Ti₂AlC by self-propagating high-temperature synthesis (SHS) with a reduction step, using titanium dioxide. We have studied the influence of synthesis conditions (starting-mixture composition and ratio of reactants) on the composition, structure, and particle size of Ti₂AlC powders. The results demonstrate that an excess of magnesium in the starting mixture leads to a decrease in the percentage of MgAl₂O₄ (spinel), and carbon deficiency in the starting mixture reduces the percentage of titanium carbide in the final product. The Ti₂AlC powders prepared by SHS consist of agglomerates of layered particles differing in size: from coarse (several microns) to ultrafine and nanometer-sized particles. The composition of the powders was confirmed by chemical analysis, microstructural examination, and X-ray diffraction.     

Facile preparation of Ag<Subscript>2</Subscript>V<Subscript>4</Subscript>O<Subscript>11</Subscript> nanoparticles via low-temperature molten salt synthesis method

Nanosized Ag₂V₄O₁₁ powders have been prepared via the low-temperature molten salt method using LiNO₃ as a reaction medium. The powders have been characterized by x-ray diffraction and transmission electron microscopy. The discharge properties of the powders have been assessed by the galvanostatic discharge test using CR2016 coin cells. The powder made at 300°C for 2 h is composed of nearly spherical particles about 40 nm in size. The discharge test shows that the powders prepared by the low-temperature molten salt method exhibit high discharge capacities.     

Low-temperature synthesis of Sr<Subscript>0.3</Subscript>Ba<Subscript>0.7</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> ultrafine powder and its characteristics

Ultrafine strontium barium niobate (Sr_0.3Ba_0.7Nb₂O₆, SBN30) powders were prepared by urea method starting from a precursor solution constituting of Sr (NO₃)₂, Ba (NO₃)₂, NbF₅, urea and polyvinyl alcohol (PVA) as surfactant. Their structural behavior and morphology were examined by means of X-ray diffractometry (XRD) and Scanning electron microscopy (SEM). The results showed that the SBN30 powders crystallized to a pure tetragonal phase at annealing temperatures as low as 750 °C. The average particle size of SBN powders subjected to 750 °C was of the order of 150–300 nm. With increasing calcination temperature,however, the average particle size of the calcined powders increased. The SBN30 ceramic prepared from urea method can be sintered at temperature as low as 1,225 °C. The transition temperature from the ferroelectric phase to the paraelectric phase and the relative dielectric permittivity of the SBN30 powder were less than the corresponding values of the bulk ceramic. The permittivity and loss tangent (tan δ) at room temperature (1 kHz) was found to be 930 and below 0.025.     

Properties of nanocrystalline ZrO<Subscript>2</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-CeO<Subscript>2</Subscript>-CoO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders

We have studied the properties of nanocrystalline ZrO₂-Y₂O₃-CeO₂-CoO-Al₂O₃ powders prepared via hydrothermal treatment of a mixture of coprecipitated hydroxides at 210°C. A number of general trends are identified in the variation of the properties of the synthesized powders during heat treatment at temperatures from 500 to 1200°C. Our results demonstrate that the addition of 0.3 mol % CoO to nanocrystalline ZrO₂-based powders containing 1 to 5 mol % Al₂O₃ allows one to obtain composites with good sinterability at a reduced temperature (1200°C).     

Morphological control of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> particles via glycothermal process

Acicular magnetite (Fe₃O₄) powders were synthesized through new glycothermal dehydration by using crystalline α-FeOOH as precursor and glycols as solvent. When ethylene glycol was used as solvent, the phase was in-situ transformed from acicular α-FeOOH to α-Fe₂O₃ and finally to Fe₃O₄ at 270 °C for 6 h without morphological change. When water was added as a co-solvent in glycothermal reaction, Fe₃O₄ powders were synthesized through dissolution–recrystallization process at 230 °C for 3 h. The volume ratio of ethylene glycol to water (E/W) in the reaction has a strong effect on the morphology of the synthesized Fe₃O₄ particles. The particle shape of Fe₃O₄ particles changed from needle to sphere when the water content in E/W volume ratio increased from 0.5 to 1 mL in mixed glycothermal condition. When the water were added by more than 10 ml, the particle shape of Fe₃O₄ changed from sphere to octahedron truncated with the {100} faces and finally distinct octahedron with only {111} faces. Also, it is demonstrated that the size of Fe₃O₄ particles can be controlled from 1–2 μm to 100–200 nm by varying the reaction conditions such as the volume ratio of water to ethylene glycol and additive in glycothermal reaction.     

Particle size dependence of optical and defect parameters in mechanically milled Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Fe₂O₃ of particle sizes ranging from 120 to 20 nm has been prepared by the ball-milling process using different milling hour. X-ray diffraction technique and transmission electron microscopy have been used for determining the average particle sizes of the prepared samples. Direct optical band gap for the unmilled and the ball-milled samples has been calculated from the optical absorption data. A red shift in the band gap due to the reduction of particle size has been observed. The coincidence Doppler broadening of the electron positron annihilation γ-radiation spectroscopy has been employed to identify the nature of defects generated due to the ball-milling process.     

Novel method of synthesis for double-perovskite Sr<Subscript>2</Subscript>FEMoO<Subscript>6</Subscript>

Polycrystalline double perovskite Sr₂FeMoO₆ nanosized powders have been prepared using a wet chemical coprecipitation method of synthesis. The products were ignited in nitrogen at different temperatures in order to examine thermal evolution of precursors. Powders that were fired at an above 850°C for two hours have almost a single-phase structure. Some intermediate phases have been found at low temperatures. Powder X-ray diffraction linewith measurements show an average particle size in the order of 40 nm for samples annealed in 600–1000°C. It is suggested that the samples annealed at these temperatures were both simultaneously paramagnetic and ferromagnetic in nature. The advantages of this method are the low temperature involve in the sample preparation and the use of a non-reducing atmosphere.     

Physical properties of lead-free BaFe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> ceramics obtained from mechanochemically synthesized powders

Modern electronics expect functional materials that are eco-friendly and are obtained with lower energy consumption technological processes. The multiferroic lead-free BaFe_1/2Nb_1/2O₃ (BFN) ceramic powder has been prepared by mechanochemical synthesis from simple oxides at room temperature. The development of the synthesis has been monitored by XRD and SEM investigations, after different milling periods. The obtained powders contain large agglomerates built by crystals with an estimated size about 12–20 nm depending on the period of milling. From this powder, the multiferroic BFN ceramic samples have been prepared by uniaxial pressing and subsequent sintering pressureless method. The morphology of the BFN ceramic samples strongly depends on high-energy milling duration. The properties of the ceramic samples have been investigated by dielectric spectroscopy, in broad temperature and frequency ranges. The high-energy milling of the powders has strongly affected the dielectric permittivity and dielectric loss of the BaFe_1/2Nb_1/2O₃ ceramic samples. The usage of the mechanochemical synthesis to obtain the multiferroic lead-free BFN materials reduces the required thermal treatment and simultaneously improves the parameters of the BFN ceramics.     

Study of Size Distribution in Nanostructured Se<Subscript>58</Subscript>Ge<Subscript>39</Subscript>Pb<Subscript>3</Subscript> Glass Using Various Characterization Methods

The present paper aims at the study of size distribution of particles in nanostructured Se₅₈Ge₃₉Pb₃ glass using X-ray diffraction (XRD), Transmission electron microscopy (TEM) and UV–visible spectrophotometer. The thin film sample has been prepared using melt quenching technique and inert gas consolidation method. The particle size distribution obtained from XRD and UV–Vis spectrophotometer shows more uncertainty than the results obtained from TEM measurements. The absorption spectra recorded on UV–Vis spectrophotometer is employed to get band gap values corresponding to different size distribution in sample. Further, it is concluded that TEM is the best measurement technique for size distribution as it has less uncertainty in the obtained results.     

Preparation of apatite-type La<Subscript>9.33</Subscript>(SiO<Subscript>4</Subscript>)<Subscript>6</Subscript>O<Subscript>2</Subscript> electrolyte by urea-nitrates combustion

Apatite-type La_9.33(SiO₄)₆O₂ powders have been prepared by urea-nitrates combustion at low temperature. Process parameters of combustion and characteristics of electrolyte were studied and optimized. Gelation time of precursor has been shortened distinctly by introducing an appropriate solvent system. Molar ratio of nitric acid to lanthanum oxide dependence of the nature of the phases has first been characterized. Well-crystallized La_9.33(SiO₄)₆O₂ powders with an average size of 30.5 nm were obtained at a calcining temperature as low as 800°C for 12h. Dense ceramic with a relative density of 96% was prepared by sintering the green compact of these nanopowders at 1400°C for 3 h. The sintering body exhibited a high ionic conductivity of 4.38 × 10⁻³ S/cm at 700°C.     

Preparation of anatase F doped TiO<Subscript>2</Subscript> sol and its performance for photodegradation of formaldehyde

Anatase fluoride doped TiO₂ sol (F-TiO₂) catalyst was prepared by a modified sol-gel hydrothermal method, using tetra butyl titanate as a precursor. The influences of F doping, temperature of hydrothermal, values of medium pH on the morphology and crystallization were studied. The microstructure and morphology of sol sample were characterized by XRD, TEM, FTIR, UV–Vis–DRS, particle size distribution (PSD) and XPS. The results showed that F-TiO₂ particles in sol were spherical and partly crystallized to anatase structure, and dispersed in the aqueous medium homogeneously and that the average particle size was ca. 10.5 nm calculated from XRD and TEM results. It was also found that the addition of fluorine could improve the crystallization and adsorption of particles significantly, the photocatalytic activity for decomposition of formaldehyde were enhanced remarkably with the doping of fluorine. Possible mechanism of anatase F-TiO₂ formed under hydrothermal conditions was discussed.     

A simple approach for the synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals

By using Co²⁺ and Co³⁺ salts, and freshly extracted ovalbumin, Co₃O₄ nanocrystals have been synthesized successfully. The pH of the solution was self-regulated for the hydrolysis of metal ions as the ovalbumin-water mixture was highly basic. Water soluble ovalbumin proteins served as a perfect matrix for entrapment of Co²⁺ and Co³⁺ ions thus forming a gel. Upon heat treatment, the dried gel precursor decomposed into nanocrystalline Co₃O₄. The crystallite size obtained by XRD line profile fitting was 45 ± 8 nm and particle size estimated from the SEM was in the range 20 nm-2 μm. EPR results show a very good fit to literature reports for nanocrystals in the size range of 8–17 nm. Even though the overall particle size is quite large and its distribution is quite wide EPR results confirm nanocrystalline nature of the particles obtained. Presented route is simple, cost effective, and environmentally friendly.     

Self-propagating high-temperature synthesis of Lu<Subscript>2</Subscript>O<Subscript>3</Subscript> powders for optical ceramics

A technique has been developed for the self-propagating high-temperature synthesis of lutetium oxide (Lu₂O₃) powders using citric acid, glycine, and lutetium acetate as fuels. We have carried out thermodynamic analysis of synthesis conditions and examined the effect of the nature of the fuel on the properties of the resultant powders. Using vacuum sintering at a temperature of 1780°C and powders prepared with glycine as a fuel and containing 25 mol % yttrium oxide and 5 mol % lanthanum oxide as sintering aids, we have obtained transparent lutetium oxide-based ceramics.     

Preparation and electrochemical properties of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> by a rheological-phase-assisted microwave synthesis method

By using LiCO₃ and MnO₂, a rheological-phase-assisted microwave synthesis method has been applied in the fast preparation of spinel LiMn₂O₄ in order to reduce the cost of cathode materials. Comparing with the pristine LiMn₂O₄ obtained by the traditional solid-state reaction method, the structure and surface morphology of the samples synthesized by the rheological-phase-assisted microwave synthesis method have been investigated. The powders were used as positive materials for lithium-ion battery, whose charge/discharge properties and cycle performance have been examined in detail. As a result, the powders prepared by the rheologicalphase-assisted microwave synthesis method at 750°C are pure spinel LiMn₂O₄ with regular shapes and uniform distribution, which exhibit higher capacity and much better reversibility than the sample prepared by the traditional solid-state reaction. The text was submitted by the authors in English.     

Synthesis of pure Zn<Subscript>2</Subscript>SiO<Subscript>4</Subscript>:Mn green phosphors by simple PVA–metal complex route

Green light emitting Zn_2−x Mn _x SiO₄ (willemite) particles were synthesized by a simple and cost-effective poly(vinyl alcohol) (PVA)-complex route. Microstructural studies on the calcined products show that particles are pure, single phase, nano-crystalline, and agglomerated morphology. A pure-phase willemite structure was obtained with calcination between 850 and 1,175 °C for 2 h in air. Particle size analysis indicates that the average particle size is ∼1 μm. The photoluminescence properties of these 4 and 12 mol% Mn-doped Zn₂SiO₄ powders were measured by fluorescence spectroscopy. Particles with 4 mol% Mn doping prepared at 1,150 °C, with an emission decay time, I ₀/e, of 13.4 ms showed the highest relative peak emission intensities. The emission intensity at this doping level was measured to be ∼110% of a representative commercial product’s, doped with 11.2 mol% Mn, and exhibiting a decay time of 7.1 ms. The effect of calcination temperature on the photoluminescence and crystallinity properties of synthesized green powders was also investigated.