Preparation of highly ordered growth of single-crystalline Gd2O2S:Eu nanostructures

A simple and facile template-assisted hydrothermal route has been demonstrated for the shape-selective preparation of highly ordered single-crystalline Gd₂O₂S:Eu³⁺ nanostructures, such as nanotubes, nanorods and nanoflowers. These fabricated nanostructures possess desirable atomic structures, surfaces, morphologies and properties to meet the growing demands and specific requirements of new technologies. The concentration of precursor chemicals, the temperature, the reaction time, and the use of a capping agent are key factors in the morphological control of Gd₂O₂S:Eu³⁺ nanostructures. The morphology and the phase composition of the prepared nanostructures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy disperse spectroscopy (EDS) and photoluminescence (PL). We believe this technique will be readily adopted in realizing other forms of various nanostructured materials.     

Size and morphology-controlled Ni2[Fe(CN)6]·xH2O Prussian Blue analogue fabricated via a hydrothermal route

Nanocrystalline Prussian Blue analogue Ni₂[Fe(CN)₆]·xH₂O was synthesized through hydrothermal process at 180 °C for 24 h with NiSO₄·6H₂O and K₄[Fe(CN)₆]·3H₂O as precursors. The effects of reactant concentration and protective matrix (Polyethylene glycol 400, PEG-400) on the size and morphology of nanoparticles were investigated. The as-synthesized products were identified as face-centered cubic structure by powder X-ray diffraction. Field-emission scanning electron microscopy and transmission electron microscopy images showed that well dispersed nanoparticles with fairly narrow size distribution were successfully prepared.     

Control of growth orientation and shape for epitaxially grown In2O3 nanowires on a-plane sapphire

Vertically aligned indium oxide nanowires were grown on a-plane sapphire substrate by the method of catalyst-assisted carbothermal reduction. The morphology and crystal structure of the nanowires are determined by X-ray diffraction, transmission electron microscopy and field-emission scanning electron microscopy. Two types of In₂O₃ nanowires were found by controlling the growth conditions. The nanowires with a hexagonal cross-section were shown to grow in [1 1 1] direction, whereas those with a square cross-section grow in [0 0 1] direction. In addition to the temperature effects, the concept of supersaturation in Au catalyst is proposed to explain the formation of these two types of nanowires. Besides, tapering, which is explained with the interplay between the vapor-liquid-solid and vapor-solid growth mechanisms, is observed in the nanowires.     

Structure study of Bi4Ti3O12 produced via mechanochemically assisted synthesis

Nanosized bismuth titanate was prepared via high-energy ball milling process through mechanically assisted synthesis directly from their oxide mixture of Bi₂O₃ and TiO₂. Only Bi₄Ti₃O₁₂ phase was formed after 3 h of milling time. The excess of 3 wt% Bi₂O₃ added in the initial mixture before milling does not improve significantly the formation of Bi₄Ti₃O₁₂ phase comparing to stoichiometric mixture. The formed phase was amorphized independently of the milling time. The Rietveld analysis was adopted to determine the crystal structure symmetry, amount of amorphous phase, crystallite size and microstrains. With increasing the milling time from 3 to 12 h, the particle size of formed Bi₄Ti₃O₁₂ did not reduced significantly. That was confirmed by SEM and TEM analysis. The particle size was less than 20 nm and show strong tendency to agglomeration. The electron diffraction pattern indicates that Bi₄Ti₃O₁₂ crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis.     

GexNbSe2 and GexNbS2 intercalation compounds

The structures of two intercalation compounds, Ge_∼0.2NbSe₂ and Ge_∼0.3NbS₂ were investigated by single crystal X-ray diffraction and electron microscopy (selected area electron diffraction (SAED), high resolution electron microscopy (HRTEM) and X-ray microanalysis by energy dispersive spectroscopy (XEDS)). Crystal structure determinations of the average structure of the intercalation compounds 2H-Ge_0.217NbSe₂ and 4H-Ge_0.288NbS₂ are reported: the selenide compound crystallizes in the space group P6₃/mmc with a = 3.4560(9) Å and c = 12.966(3) Å and adopts the 2H-NbSe₂ structure-type, while the sulfide compound crystallizes in the P6₃mc space group, with a = 3.3392(9) Å and c = 25.404(7) Å with a structure-type 4H_c-NbS₂ which it is known for TaSe₂. In both structures the germanium atoms are located in the empty octahedral positions of the van der Waals gap between the NbX₂ (X = S, Se) layers. Electron diffraction patterns from several Ge_xNbSe₂ crystal flakes show different superstructures and exhibit diffracted diffuse intensity: weak satellites corresponding to and 2a₀ × 2a₀ superstructures were observed for x ∼ 0.15 (a₀ is the basal lattice parameter of the host structure). For x ∼ 0.25-0.33, the same type of satellite is observed with a stronger intensity. For x ∼ 0.5 only satellites corresponding to the superstructure were present. In the case of Ge_xNbS₂, with 0.10 < x < 0.25, the germanium atoms are ordered in domains with an superstructure. In some crystals disorder along the c-axis has been observed.     

Low-temperature performance of Al4B2O9 nanowires

In this paper we report on the synthetic investigation of single-crystalline aluminum borate (Al₄B₂O₉) nanowires in large scale by a direct calcination of a precursor powder made of Na₂B₄O₇·10H₂O and Al (NO₃)₃·9H₂O at a low temperature of 850 °C. The nanowires, with the diameter of 20-40 nm and the length up to several micrometers, possess smooth surfaces and uniform sizes along the entire wire. The growth mechanism of the nanowires is attributed to a solid-liquid-solid process, which controls the nanowire morphology.     

Shape evolution of Cu2S nanostructures in Triton X-100/cyclohexane/water reverse micelles

The shape evolution of Cu₂S nanostructures, which were produced in Triton X-100/cyclohexane/water reverse micelles, was investigated by the transmission electron microscopy technique as a function of aging time, and the effect of the molar ratio of water to surfactant on the size and shape of Cu₂S nanostructures was also discussed. The results suggest that at the initial stage the nucleation process was dominant and the shape of Cu₂S nanostructures was preferably confined by the reverse micelle droplets and took spherical forms. With the extension of the aging time, the growth gradually governed the process and the shape of Cu₂S nanostructures evolved first to nanorods, and then to nanowires gradually. The formation of one-dimensional Cu₂S nanostructures is attributed to a directed aggregation growth process mediated by reverse micelle droplets, which was confirmed by high-resolution transmission electron microscopy. Furthermore, the size and shape of Cu₂S nanostructures can be controlled by changing the molar ratio of water to surfactant.     

Structural study by X-ray diffraction and transmission electron microscopy of the misfit compound (SbS1−xSex)1.16(Nb1.036S2)2

In the Sb-Nb-S-Se system, a new misfit layer compound (MSL) has been synthesized and its structure was determined by combining single crystal X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It presents a composite crystal structure formed by (SbS_1−xSe_x) slabs stacking alternately with double NbS₂ layers and both can be treated as separate monoclinic subsystems. The (SbS_1−xSe_x) slabs comprise a distorted, two-atom-thick layer with NaCl-type structure formed by an array of {SbX₅} square pyramids joined by edges (X: S, Se); the NbS₂ layers consist of {NbS₆} trigonal prisms linked through edge-sharing to form sheets, just as in the 2H-NbS₂ structure type. Both sublattices have the same lattice parameters a = 5.7672(19) Å, c = 17.618(6) Å and β = 96.18(3)°, with incommensurability occurring along the b direction: b₁ = 3.3442(13) Å for the NbS₂ subsystem and b₂ = 2.8755(13) Å for the (SbS_1−xSe_x) subsystem. The occurrence of diffuse scattering intensity streaked along c^* indicates that the (SbS_1−xSe_x) subsystem is subjected to extended defects along the stacking direction.     

Study on the structures and magnetic properties of Ni, Co-Al2O3 electrodeposited nanowire arrays

We report on the direct electrodeposition of nickel and cobalt nanowire arrays within the nanopores of ordered porous alumina films prepared by a two-step anodization. SEM and TEM images reveal that the pore arrays are regularly arranged throughout the alumina film. X-ray diffraction and TEM analysis show that the nickel and cobalt nanowires are single crystalline with highly preferential orientation. The aspect ratio of nanowires is over 300. M-H hysteresis loops determined by VSM indicate that the nanowire arrays obtained possess obvious magnetic anisotropy. Because of proper square ratio and coercivity the nanowire arrays of nickel seem to be more suitable candidates for perpendicular magnetic recording medium than those of cobalt.     

Ba2.1Bi0.9(O, F)6.8−δ: A new ordered anion-excess fluorite

The anion-excess ordered fluorite-related phase Ba_2.1Bi_0.9(O, F)_6.8−δ has been synthesized by a solid state reaction of BaF₂, BiF₃ and Bi₂O₃ at 873 K with subsequent short annealing at 573 K. The crystal structure of the new phase has been solved using electron diffraction and X-ray powder diffraction (a = 9.5372(1) Å, c = 18.1623(3) Å, space group I4/m, R_I = 0.025, R_P = 0.029). Interstitial anions in the fluorite-based structure are considered to form isolated cuboctahedral 8:12:0 clusters. The structural relationship between the oxyfluoride phase Ba_2.1Bi_0.9(O, F)_6.8−δ and similar rare-earth-based fluorides is discussed.     

Nanorod alumina-supported Ni-Zr-Fe/Al2O3 catalysts for hydrogen production in auto-thermal reforming of ethanol

Nanorod alumina-supported Ni-Zr-Fe/Al₂O₃ catalysts were prepared by co-impregnation, characterized by TEM, TPR, XRD, XPS, and TPD-pyridine, and tested in auto-thermal reforming of ethanol. The characterization results indicate that, with iron and zirconia promotion, the Ni_xFe_1−xAl₂O₄ mixture spinel forms, the valence of the surface Ni species is modified, and the acidity decreases. As a result, during a 30-h test over the Ni-Zr-Fe/Al₂O₃ catalyst, sintering is restrained, and the selectivity to hydrogen remains around 85.79% without obvious loss, while the un-promoted Ni/Al₂O₃ shows poor stability and selectivity.     

Structural properties of Al2O3-La2O3 binary oxides prepared by sol-gel

The structural properties of La₂O₃ and Al₂O₃-La₂O₃ binary oxides prepared by sol-gel were studied by XRD, HRTEM and UV-vis. The binary oxides with high lanthana contents show an amorphous structure after calcination at 650 °C. At calcination temperatures higher than 1000 °C there is a phase transformation from the amorphous state to the crystalline LaAlO₃ with a perovskite structure. The structure of La₂O₃ is consistent with the hexagonal system; however, some crystalline microdomains with a monoclinic structure were detected by HRTEM. Islands of La₂O₃ and LaAl₁₁O₁₈ phases were detected at high lanthana concentration in the binary oxide. The modification in the coordination shell of the Al³⁺ cations due to the interaction with La³⁺ cations confirms the formation of phases with a perovskite structure and the presence of islands of the LaAl₁₁O₁₈ phase.     

One-pot synthesis of CuFeSe2 cuboid nanoparticles

Ternary semiconducting CuFeSe₂ nanocrystals of a particular shape and size were successfully synthesized using a cost-effective and simple one-pot chemical route. X-ray powder diffraction and field emission scanning electron microscopy results indicated that the as-synthesized CuFeSe₂ comprised cuboid nanoparticles with dimensions of 50–150 nm as well as a tetragonal phase. Elemental analysis yielded an atomic ratio of Cu:Fe:Se of 1:1.06:2.17. The synthesis temperature and the solvent octadecylamine were significant in determining the structural phases and morphologies of the final products. The optimal condition for synthesizing the tetragonal CuFeSe₂ phase with cuboid nanoparticles was a reaction temperature of 200 °C for 1 h in octadecylamine solvent. A possible mechanism of the formation of ternary CuFeSe₂ nanoparticles with controllable shapes is discussed.     

Thermal behavior of the amorphous precursors of the ZrO2-SnO2 system

Thermal behavior of the amorphous precursors of the ZrO₂-SnO₂ system on the ZrO₂-rich side of the concentration range, prepared by co-precipitation from aqueous solutions of the corresponding salts, was monitored using differential thermal analysis, X-ray powder diffraction, Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectrometry (EDS). The crystallization temperature of the amorphous precursors increased with an increase in the SnO₂ content, from 405 °C (0 mol% SnO₂) to 500 °C (40 mol% SnO₂). Maximum solubility of Sn⁴⁺ ions in the ZrO₂ lattice (∼25 mol%) occurred in the metastable products obtained upon crystallization of the amorphous precursors. A precise determination of unit-cell parameters, using both Rietveld and Le Bail refinements of the powder diffraction patterns, shows that the incorporation of Sn⁴⁺ ions causes an asymmetric distortion of the monoclinic ZrO₂ lattice. The results of phase analysis indicate that the incorporation of Sn⁴⁺ ions has no influence on the stabilization of cubic ZrO₂ and negligible influence on the stabilization of tetragonal ZrO₂. Partial stabilization of tetragonal ZrO₂ in products having a tin content above its solid-solubility limit was attributed to the influence of ZrO₂-SnO₂ surface interactions. In addition to phases closely structurally related to cassiterite, monoclinic ZrO₂ and tetragonal ZrO₂, a small amount of metastable ZrSnO₄ phase appeared in the crystallization products of samples with 40 and 50 mol% of SnO₂ calcined at 1000 °C. Further temperature treatments caused a decrease in and disappearance of metastable phases. The results of the micro-structural analysis show that the sinterability of the crystallization products significantly decreases with an increase in the SnO₂ content.     

Crystal growth and structure determinations of potassium hafnates: K2Hf2O5 and K4Hf5O12

Crystals of K₂Hf₂O₅ and K₄Hf₅O₁₂ were grown from molten potassium hydroxide flux. The crystal structures were determined by single-crystal X-ray diffraction. K₂Hf₂O₅ crystallizes in the space group Pnna of the orthorhombic system, with unit cell dimensions of a = 5.780(1) Å, b = 10.640(2) Å, and c = 8.666(2) Å. This compound contains infinite chains of HfO₆ octahedra that form a channel structure. K₄Hf₅O₁₂ crystallizes in the space group of the trigonal system, with unit cell dimensions of a = 5.7877(2) Å and c = 10.3693(7) Å. This compound possesses a layered structure with six-coordinate Hf in three different coordination environments (trigonal prismatic, distorted octahedral, and regular octahedral).     

High temperature annealing of micrometric Zn2SiO4:Mn phosphor powders in fluidized bed

Micrometric Zn_1.8Mn_0.2SiO₄ phosphor powders prepared by spray pyrolysis have been annealed between 900 and 1200 °C under ambient air atmosphere to investigate their luminescence properties. Two original gas-solid fluidization processes have been tested in order to limit sintering phenomena, and the post-treated products have been compared with those annealed using a conventional process in crucible. The crystallinity, the size distribution, the outer morphology and the luminescence properties of powders before and after treatment have been analysed. Massive sintering phenomena occur in crucible from 1000 °C, whereas the original granulometry and spherical morphology are preserved till 1100 °C in fluidized bed. The luminescence efficiencies are comparable for the three processes and shown to be maximal after annealing at 1200 °C. It has been established that residual ZnO and manganese ions at oxidation state higher than 2+, still present after treatment at 1100 °C, are detrimental to good luminescence efficiency. Both disappear from samples post-treated at 1200 °C.     

Subsolidus phase equilibria in the Al2O3-CeO2-PbO and Al2O3-CeO2-RuO2 systems

The subsolidus phase equilibria in air for the Al₂O₃-CeO₂-PbO and Al₂O₃-CeO₂-RuO₂ systems were studied with the aim of obtaining information on possible interactions between a CeO₂-based solid electrolyte in solid-oxide fuel cells (SOFCs) and other oxides. No ternary compound was found in either of the systems. The tie line in the Al₂O₃-PbO-CeO₂ system is between Al₂Pb₂O₅ and the CeO₂.     

Synthesis of stable spherical platinum diphosphide, PtP2/carbon nanocomposite by reacting Pt(PPh3)4 at elevated temperature under autogenic pressure

The synthesis of microsized carbon spheres supporting the semiconductor platinum diphosphide, PtP₂, was conducted by the thermal decomposition of an organometallic precursor. This novel reaction was carried out using the reaction under autogenic pressure at elevated temperature (RAPET) method by dissociating Pt(PPh₃)₄ at 1000 °C. The product was characterized using methods of electron microscopy (scanning electron microscope (SEM), transmission electron microscope (TEM), selected area energy dispersive spectroscopy (SAEDS), elemental analyzer (EA) and energy dispersive X-ray analysis (EDX)) and powder-XRD. Transmission electron microscope images indicate that the particle size of the nanoparticles of PtP₂ coated on the carbon spheres is 50 nm.     

Structural and magnetic characterization of LiMn1.825Cr0.175O4 spinel obtained by ultrasonic spray pyrolysis

Quaternary spinel oxide LiMn_1.825Cr_0.175O₄ powder was synthesized by using an ultrasonic spray pyrolysis method, without additional annealing. The crystal structure of the as-prepared powder was revealed by X-ray powder diffraction and identified as a single spinel phase with Fd3m space group. The powders had a spherical morphology with extremely smooth surface appearance and densely congested interior structure. Transmission electron microscopy confirmed that the particle consisted by the cohesion of the primary particles. Magnetic measurements performed in DC field in both zero-field-cooled and field-cooled regimes, as well as AC susceptibility experiments, show that system undergoes spin-glass transition at the freezing temperature T_f = 20 K. The value of the effective magnetic moment μ_eff = 4.34 μ_B obtained from the Curie-Weiss fit in the high temperature region confirms the substitution of Mn³⁺ ions with Cr³⁺ ions.     

Crystal structures of CdTi2O4(OH)2 and LaTiSbO6

The crystal structures of two PbSb₂O₆-type compounds containing titanium, CdTi₂O₄(OH)₂ and LaTiSbO₆ were refined by X-ray powder diffraction data. For both compounds structure refinements with the space group were successful and the R-factors were R_WP = 6.46% and R_P = 4.90% for CdTi₂O₄(OH)₂ and R_WP = 9.55% and R_P = 7.17% for LaTiSbO₆. These crystal structures were the same as that of the typical PbSb₂O₆-type compound in spite of the existence of protons in the interlayer or two different metal ions in the layer.