Ionic liquid‐assisted hydrothermal synthesis of γ‐Al2O3hierarchical nanostructures

The boehmite (Al₂O₃·H₂O) hierarchical nanostructure with spindle‐like morphology has been successfully synthesized via ionic liquid‐assisted hydrothermal synthetic method under mild condition using an ionic liquid 1‐butyl‐3‐dimethylimidazolium bromide ([Bmim][Br]) as a template. The proposed formation mechanism has been investigated and the hydrogen bond‐co‐π–π stack mechanism is used to be responsible for the present formation of the precursor hierarchical nanostructure. The γ‐Al₂O₃ hierarchical nanostructure was obtained by calcining the as‐synthesized precursor at 500 °C for 2 h, preserving the same morphology. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

synthesis of high‐quality crystalline α‐MoO3 nanobelts

High‐quality crystalline MoO₃ nanobelts were successfully fabricated with a facile hydrothermal route by using common and inexpensive NaCl as a capping agent. The products are thoroughly characterized by the combination of different techniques. The results indicate that as‐prepared MoO₃ nanobelts have an orthorhombic crystal structure (α‐MoO₃) with growth preferential in the [001] direction, the size of the obtained MoO₃ nanobelts ranges from 200 nm to 300 nm in width and micrometers in length. The effects of the amount of NaCl on the morphology and size of the resultant MoO₃ were also investigated, it is clearly shown that the presence of appropriate amount of NaCl plays a crucial role in controlling the size and morphology of the obtained MoO₃. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic field dependence of the relative critical current density in γ‐irradiated polycrystalline YBa2Cu3O7

The effect of different doses of γ‐rays on the behavior of the critical current density, J_c in an YBa₂Cu₃O₇ polycrystalline sample has been investigated at high temperatures. The samples were irradiated at room temperature by a ⁶⁰Co γ‐ray source at a dose rate of 0.5 MR/h. J_c was found to increase significantly with after irradiation dose of 10 MR. Further irradiation dose of 50 MR produced a slight and field dependent enhancement of J_c above its values at 10 MR. The most interesting result is that the relative change in the critical current density was found to have a non‐monotonic behavior with the applied magnetic field. These results are discussed in terms of the roles of several mechanisms created by γ‐rays in the regions of the grain boundaries combined with the effect of the magnetic field on these mechanisms. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of γ‐irradiation on spectral properties of undoped Y2SiO5 crystals

The absorption spectra of undoped Y₂SiO₅ crystals were studied before and after γ‐irradiation. After γ‐irradiation, the additional absorption peaks at 260‐270 and 320nm were observed in as‐grown and H₂‐annealed Y₂SiO₅ crystal, but it did not occur in air‐annealed Y₂SiO₅ crystal. These absorption peaks were attributed to F color centers and O^– hole centers, respectively. Owing to more oxygen vacancies and color centers in H₂‐annealed Y₂SiO₅ crystal than that in as‐grown Y₂SiO₅ crystal after γ‐irradiation, the additional absorption peaks were more intense in the former than that in the latter. With the irradiation dose increasing from 20 to 220kGy, the intensity of additional absorption peaks increased. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Facile hydrothermal synthesis of uniform 3D γ‐AlOOH architectures assembled by nanosheets

Uniform γ‐AlOOH architectures assembled by nanosheets were successfully synthesized in the mixture of deinonized water and dimethyl sulfoxide (DMSO) at 180 °C. The structure and morphology of products were characterized by X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The products displayed 3D microstructures with its length of 1 μm and diameter of 400‐500 nm. The obtained γ‐AlOOH structures exhibited large Brunauer‐Emmett‐Teller (BET) surface area of 216.5 m²/g and pore size of 3.7 nm. The formation mechanism of 3D γ‐AlOOH architectures was also discussed based on the experimental results. Furthermore, the γ‐AlOOH architectures exhibited preliminary photoluminescence (PL) phenomenon with a strong peak at 323 nm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects induced by chemical non‐stoichiometry and γ‐irradiation on the habit and unit cell parameters of ammonium tetrachlorozincate

The effect of chemical non‐stoichiometry and γ‐irradiation on the unit cell parameters of ammonium tetrachlorozincate (NH₄)₂ZnCl₄ (A₂ZC₄) has been studied. The unit cell parameters of crystal grown from solution with NH₄Cl/ZnCl₂ molar ratio 1:1, apparently non‐stoichiometrric, are nearly the same as those given for ammonium tetrachlorozincate in the literature. The 2:1 ratio is actually ‘pseudo‐stoichiometric’ due to the hygroscopic nature of ZnCl₂. The unit cell parameters of crystal grown from solution with molar ratio 2:1 match those of the structure (NH₄)₃ZnCl₅ (A₃ZC₅). The habit of the crystal grown in the former case, from solution with excess ZnCl₂, was different from that of the crystal grown in the later case, from solution with excess (NH₄)Cl. Between these two limits, a set of four samples were prepared from solutions with an excess of ZnCl₂ of 20, 30, 60 and 80 wt% in order to detect exact stoichiometric composition to grow A₂ZC₄. Analysis by X‐ray diffraction shows that the first two crystals out of this set are mixed from A₂ZC₄ and A₃ZC₅ The third and fourth crystals still contain traces of A₃ZC₅. Analysis of the X‐ray diffraction was then confirmed by DTA study. Irradiating A₂ZC₄ with γ‐dose of 250 kGy slightly increased the unit cell volume due to imperfections created by irradiation. Two computer programs were used to calculate the lattice constants and the results were compared. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solution growth and morphology of CH3NH3PbBr3 single crystals in different solvents

In this work, large‐sized CH₃NH₃PbBr₃ single crystals were successful grown using solution evaporation method with hydrohalic acid and N, N‐Dimethylformamide (DMF) as solvent respectively. The lattice parameters of cubic CH₃NH₃PbBr₃ were estimated using XRD method. The solubility of CH₃NH₃PbBr₃ in hydrobromic acid was determined at the temperature range between 20 °C–90 °C. A special micro‐solution crystallizer was designed to in‐situ study the morphology of CH₃NH₃PbBr₃ crystal. The largest crystal face was indexed by the XRD patterns and it would be {110} for CH₃NH₃PbBr₃ grown from HBr solution and {100} from DMF solution. The results show that solvent would affect the morphology and crystal habit greatly during crystal growth from solution.     

Capsule‐like α‐Fe2O3 nanoparticles: Synthesis,characterization, and growth mechanism

Uniform capsule‐like α‐Fe₂O₃ particles were synthesized via a simple hydrothermal method, employing FeCl₃ and CH₃COONa as the precursors and sodium dodecyl sulfate (SDS) as soft template. X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and high‐resolution transmission electron microscopy were used to characterize the structure of synthesized products. Some factors influencing the formation of capsule‐like α‐Fe₂O₃ particles were systematically investigated, including different kinds of surfactants, the concentration of SDS, and reaction times. The investigation on the evolution formation reveals that SDS was critical to control the morphology of final products, and a possible five‐step growth mechanism was presented by tracking the structures of the products at different reaction stages.     

Recharging processes of Cr ions in Mg2SiO4 and Y3Al5O12 crystals under influence of annealing and γ ‐ irradiation

Recharging processes of chromium ions were investigated for Mg₂SiO₄:Mg, Cr single crystals using annealing in O₂ and in air and γ‐irradiation, as compare to YAG :Ca, Cr single crystals. The formation of tetravalent Cr ions in the Mg₂SiO₄ :Mg, Cr is related not only to the initial Cr content in the melt, oxygen partial pressure and O₂‐ vacancy existing in the crystal, but also to the external field such as γ‐irradiation. The additional absorption after γ‐irradiation shows the decrease in intensity of the absorption of Cr³⁺ and Cr⁴⁺ ions in some part of the spectrum and increase in the other giving evidence on recharging effects between Cr³⁺ and Cr⁴⁺. There arises also color centers observed between 380 nm and 570 nm that may participate in energy transfer of any excitation to Cr⁴⁺ giving rise to Cr⁴⁺ emission. Opposite to forsterite crystal, absorption spectrum of YAG:Ca, Cr crystal after γ‐irradiation reveals only increase in the absorption of the Cr bands. The observed behavior of the absorption spectrum of YAG:Ca, Cr crystal under influence of γ‐irradiation suggests that γ‐irradiation ionizes only Cr ions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Morphological Changes and Twinning of ZnS (Sphalerite) Crystallites under Hydrothermal Conditions

Morphological characteristics and twinning mechanism of ZnS crystals under hydrothermal conditions have been investigated in this paper. It was shown that under hydrothermal conditions the morphology of ZnS crystallites changes along the four‐fold axis directions, and the crystals are observed in a positive or negative tetrahedron, or in a combination of positive and negative tetrahedra depending on the growth conditions. The positive tetrahedral areas on the crystallites get larger with increase of the concentrations of OH^‐ and S^2‐ in solutions, whereas the twinned crystallites of ZnS taking an elliptic shape with (111) as composition plane are easily formed in weak basic solutions. It can be found that the morphologies of ZnS crystals are in accordance with the crystallization orientations of positive or negative coordination tetrahedra ([S‐Zn₄]⁶⁺, [Zn‐S₄]^6‐) in the crystal although, in some cases, the practical morphology could be greatly affected by growth conditions, and the twinning mechansim can be suggested based on the linkage of growth units of positive and negative coordination tetrahedra, which were formed in the solution. The present investigations further indicated that the crystal chemistry approach based on the linkage/incorporation of growth units previously proposed by us can be sucessfully applied to interpret the growth mechanisms of the crystals and to control a desirable morphology.     

Spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated bis(acetylacetonato)palladium(II)

This paper reports on a theoretical analysis of spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated Pd(II)(acac)₂. Through the crystal‐ and ligand‐field theory, the microscopic spin‐Hamiltonian parameters and local molecular structure for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system have been studied by using the high‐order perturbation formulas and Newman's superposition model. Based on these calculations, it was found that the distance of the metal‐ligand bonds in the square planar complex for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system increases by 0.1Å. To understand the detailed physical and chemical properties of the [Pd(I)(acac)₂]^2– complex, the contributions of the spin‐orbit coupling of ligand to spin‐Hamiltonian parameters for Pd(I) ion are considered. The theoretical results are in reasonable agreement with the experimental values. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of large La1‐xPbxMnO3+δ (x=0.32–0.35) crystals

Large crystals of La_0.63Pb_0.37Mn O_3+δ with small La(Pb)‐ deficiency of about 0.005‐0.01 at.% were grown by high temperature solution growth method. The structure of the grown crystals was determined as rhombohedral with R‐3 space group by single‐crystal X‐ray diffractometry. The surface morphology of the crystals and the exact chemical composition was examined by scanning electron microscopy and energy dispersive X‐ray analysis methods, respectively. The IR‐transmission spectrum reveals the presence of Mn³⁺O₆‐ and Mn⁴⁺O₆‐ octahedra in the lattice of La_0.63Pb_0.37Mn O_3+δ crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of ytterbium tartrate trihydrate crystals in silica and agar‐agar gels and their characterization

Single crystals of ytterbium tartrate trihydrate have been grown by gel method using silica and agar‐agar gels as media of growth. The medium of growth influences the morphology of grown crystals, silica gel yielding single and polycrystalline in the form of spherulites whereas agar‐agar gel leading to growth of single and twinned crystals. Materials grown as single crystals have been characterized by using optical and scanning electron microscopy (SEM), EDAX, XRD, FT‐IR, CHN and thermogravimetric techniques. The stoichiometry of the grown single crystals is suggested to be Yb(C₄H₄O₆) (C₄H₅O₆).3H₂O. The FT‐IR spectrum shows the presence of singly as well as doubly ionized tartrate ligands. Results of thermal analysis indicate that the material is thermally stable up to a temperature of 200 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Mn(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions: I. Growth habit and surface morphology

The effect of concentration of Mn(II) ions on the growth habit and the surface micromorphology of different as‐grown faces of ammonium oxalate monohydrate (AO) single crystals grown from aqueous solutions was studied at a constant temperature of 30 °C and predefined supersaturations up to 20%. It was observed that the growth habit and the surface morphology of the crystals strongly depend on the supersaturation used for growth and the impurity concentration in the solution. The experimental results were analysed in terms of connected nets determined from different projections of the structure of AO crystals. Analysis of the observations revealed that: (1) the directions of connected nets corresponding to basic growth units composed of single (NH₄)₂C₂O₄ · H₂O molecules are in excellent agreement with the low‐index crystallographic directions of the orientations of growth layers, (2) all faces appearing in the growth morphology of AO crystals are F faces, and (3) the {001} face growing from pure aqueous solutions is essentially a kinetically rough face but the presence of Mn(II) impurity leads to their appearance in the morphology due to increase in the strength of bonds of the connected nets composing the surface graph.     

Growth and characterization of Nd,Yb – yttrium oxide nanopowders obtained by sol‐gel method

Nanopowders of Y₂O₃ pure, doped and codoped by Nd³⁺, Yb³⁺ were obtained by sol‐gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one‐phased compounds of Y₂O₃ doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y₂O₃ doped 0.5 at% Nd and 2 at% Yb are presented. Y₂O₃ containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co‐doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low‐temperature urea‐assisted hydrothermal synthesis of Bi2S3 nanostructures with different morphologies

Different morphologies of single‐crystalline orthorhombic phase bismuth sulfide (Bi₂S₃) nanostructures, including sub‐microtubes, nanoflowers and nanorods were synthesized by a urea‐assisted hydrothermal method at a low temperature below 120 °C for 12 h. The as‐synthesized powders were characterized by X‐ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and UV‐vis spectrophotometry. The experimental results showed that the sulfur sources had a great effect on the morphology and size of the resulting powders. The formation mechanism of the Bi₂S₃ nanostructures with different morphologies was discussed. All Bi₂S₃ nanostructures showed an appearance of blue shift relative to the bulk orthorhombic Bi₂S₃, which might be ascribed to the quantum size effect of the final products. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,characterization and crystal structure of a novel Ni(II) coordination polymer with dipyrido[3,2‐a:2′,3′‐c]phenazine and 4,4′‐oxy(bisbenzoate)

A novel coordination polymer, [Ni(dppz)(oba)(H₂O)]·0.5H₂O (dppz = dipyrido[3,2‐a:2′,3′‐c]phenazine and oba = 4,4′‐oxy(bisbenzoate)) has been synthesized through hydrothermal method and characterized by IR, and single‐crystal X‐ray diffraction. It crystallizes in monoclinic, space group C2/c with a = 23.163(5), b = 18.211(4), c = 14.460(3) Å, α = γ = 90°, β = 100.45(3)°, V = 5998(2) ų, Z = 2. The structure was solved by direct methods and refined to R = 0.0866 (wR₂ = 0.1836). The compound exhibits interesting one‐dimensional chain structures, which are further stacked through π‐π interactions to form supramolecular double chains. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characteristics of the binary faceted eutectic: benzoic acid – salicylic acid system

The consistent symmetry relations computed from the heterogeneous nucleation data of the non‐ideal benzoic acid – salicylic acid eutectic system verifies the validity of nucleation theory. The kinetics of crystal growth from the molten state of the system follows the dislocation mechanism. Anomalous behaviour of both viscosity and activation energy for the eutectic melt confirms the essence of specific interactions animating molecular clusters rich in predominating eutectic phase. Micromorphology of the system obeys the Hunt‐Jackson model. The plot between a mechanical property and variable anisotropic growth velocity for the eutectic composite evidentially complies with the Weibull probability distribution curve. The curve is perused with two cut‐off points corresponding to a lower strength limit in the slow and fast growth regions and an upper strength limit in the moderate growth region. The latter aspect reveals the theoretical strength of the eutectic crystallites. The strength‐growth relationship explicated thereby is linear, optimum and linear respectively in the slow, moderate and fast growth regions of solidification. The moderate anisotropic growth (∼2.96 X 10^‐7m³s^‐1) is of greater interest by virtue of its attribute to unifying and organizing the crystallites parallel to each other in the growth direction. The eutectic composite material obtained by this process attains remarkable superiority in the mechanical properties over its isotropic growth in an ice bath (∼273 K), and its constituent phases. The co‐relation between excess thermodynamic functions indeed predicting the liquidus character and the microstructural parameters inevitably structuring the morphology is presented. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal synthesis of ultralong single‐crystalline α‐Ni(OH)2 nanobelts and corresponding porous NiO nanobelts

Ultralong α‐Ni(OH)₂ nanobelts with uniform size have been prepared on large scale via a facile template‐free hydrothermal method. The as‐prepared nanobelts were single crystals, with several tens of microns in length and about 100 nm in width. For the whole process, a novel nucleation–aggregation–dissolution–seed‐directed growth mechanism was proposed based on the experimental results. The roles of aqueous ammonia and hydrothermal temperature were also discussed. Furthermore, porous NiO nanobelts were obtained by annealing the as‐prepared Ni(OH)₂ nanobelts. This facile, template‐free, and low cost method might feasibly be scaled up for industrial production. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase‐manipulable synthesis of Cu‐based nanomaterials using ionic liquid 1‐butyl‐3‐methyl‐imidazole tetrafluoroborate

Using the ionic liquid (IL), 1‐butyl‐3‐methyl‐imidazole tetrafluoroborate, and the precursor Cu₇Cl₄(OH)₁₀·H₂O, series of phase‐manipulable Cu‐based nanomaterials were synthesized by hydrothermal and microwave assisted routes, respectively. The structural characters of the as‐prepared CuO, CuO/Cu₂O composites and pure Cu nanoparticles were investigated by XRD, SEM, TEM and HRTEM, and their surface photovoltaic properties were studied by surface photovoltage spectra. Via hydrothermal route Cu²⁺ ions were found to be reduced gradually into Cu⁺ and subsequently Cu⁰ with increasing the IL, and various phase ratio of CuO, Cu₂O and Cu composite nanosheets and pure Cu nanoparticles were obtained. This implies that the IL could function as both a reductant in the oxygen‐starved condition and a template for the nanosheet products. The ¹H‐NMR result of the IL supports it being a reductant. In microwave assisted route, however, only monoclinic single crystalline CuO nanosheets were obtained, which indicates the IL being a template only in oxygen‐rich condition. Therefore, the crystal phase, composition and morphology of the Cu‐based products could be controlled by simply adjusting the quantity of the IL and oxygen in solution routes. The molecular structure of the IL after oxidation reactions was investigated by ¹H‐NMR and a possible reaction mechanism was proposed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)