Showing papers in "Crystal Research and Technology in 2013"
TL;DR: MoS2 nanosheets with controllable morphologies were successfully synthesized via a novel mixed-solvothermal approach based on interfusing organic solvent in the solution as discussed by the authors.
Abstract: MoS2 nanosheets with controllable morphologies were successfully synthesized via a novel mixed–solvothermal approach based on interfusing organic solvent in the solution The morphology of the MoS2 nanosheets was lamellar–like using the mixed water/ethanol/N–Methyl pyrrolidone solvents, whereas that prepared with the mixed water/ethano/ethylene glycol solvents changes to fullerene–like Because of the structure-directing ability of organic molecules, the mixed solvents were proposed to be responsible for the formation of such different morphologies The average size of MoS2 nanosheets was approximately 90 nm, and the thickness was about 10–20 nm The results indicated that the crystalline phase and morphology were largely influenced by calcination and reaction system
71 citations
TL;DR: In this article, a modified Pechini method was used to obtain Mg-doped ZnO thin films with different Mg doping contents (0, 3, 5, 8, 10, and 12%).
Abstract: ZnO thin films with different Mg doping contents (0%, 3%, 5%, 8%, 10%, respectively) were prepared on quartz glass substrates by a modified Pechini method. XRD patterns reveal that all the thin films possess a polycrystalline hexagonal wurtzite structure. The peak position of (002) plane for Mg-doped ZnO thin films shifts toward higher angle due to the Mg doping. The crystallite size calculated by Debey-Scherrer formula is in the range of 32.95–48.92 nm. The SEM images show that Mg-doped ZnO thin films are composed of dense nanoparticles, and the thickness of Mg-doped ZnO thin films with Mg doped at 8% is around 140 nm. The transmittance spectra indicate that Mg doping can increase the optical bandgap of ZnO thin films. The band gap is tailored from 3.36 eV to 3.66 eV by changing Mg doping concentration between 3% and 10%. The photoluminescence spectra show that the ultraviolet emission peak of Mg-doped ZnO thin films shifts toward lower wavelength as Mg doping content increases from 3% to 8%. The green emission peak of Mg-doped ZnO thin films with Mg doping contents were 3%, 8%, and 10% is attributed to the oxygen vacancies or donor-acceptor pair. These results prove that Mg-doped ZnO thin films based on a modified Pechini method have the potential applications in the optoelectronic devices.
53 citations
TL;DR: In this paper, the structural and physical properties at different scales of Portland Cement are assessed from the point of view of the processes at the molecular scale, and state of the art problems and trends in cement studies are briefly assessed.
Abstract: Portland cement is a fundamental structural and binding material for industry and society. Its structural and physical properties at different scales show a complexity that can presently be barely managed through experimental and computational methods. State of the art problems and trends in cement studies will be briefly assessed from the point of view of the processes at the molecular scale.
42 citations
TL;DR: In this paper, a fast and facile microwave-assisted hydrothermal process was used to synthesize ZnO nanostructures with various morphologies including rod-like, sheet-like and needle-like structures.
Abstract: ZnO nanostructures with various morphologies including rod-like, sheet-like, needle-like and flower-like structures were successfully synthesized via a fast and facile microwave-assisted hydrothermal process. Reaction temperature, reaction time and the addition of NaOH were adjusted to obtain ZnO with different morphologies. Scanning electron microscopy(SEM), transmission electron microscope(TEM), X-ray diffraction (XRD) and ultraviolet spectrophotometer (UV) were used to observe the morphology, crystal structure, ultraviolet absorption and photocatalytic activity of the obtained ZnO. The results indicated that growth rate of ZnO nanostructure along [001] direction was more sensitive to temperature compared with those along [101] and [100] directions. The competition between anionic surfactant and OH− played an important role in the formation of ZnO with various morphologies. Flower-like ZnO had better ultraviolet absorption property and excellent photocatalytic activity than ZnO in the other morphologies. On the basis of the above results, a possible growth mechanism for the formation of ZnO nanostructures with different morphologies was described.
33 citations
TL;DR: Mg-doped ZnO (MgxZn1-xO) nanoparticles with precise stoichiometry are synthesized through polyacrylamide polymer method.
Abstract: Mg-doped ZnO (MgxZn1-xO) nanoparticles with precise stoichiometry are synthesized through polyacrylamide polymer method. Calcination of the polymer precursor at 650 °C gives particles of the homogeneous solid solution of the (MgxZn1-xO) system in the composition range (x < 0.15). ZnO doping with Mg causes shrinkage of lattice parameter c. The synthesized MgxZn1-xO nanoparticles are typically with the diameter of 70–85 nm. Blue shift of band gap with the Mg-content is demonstrated, and photoluminescence (PL) from ZnO has been found to be tunable in a wide range from green to blue through Mg doping. The blue-related PL therefore appeared to be caused by energetic shifts of the valence band and/or the conduction band of ZnO. MgxZn1-xO nanoparticles synthesized by polyacrylamide-gel method after modified by polyethylene glycol surfactant have a remarkable improvement of stability in the ethanol solvent, indicating that these MZO nanoparticles could be considered as the candidate for the application of solution–processed technologies for optoelectronics at ambient temperature conditions.
33 citations
TL;DR: In this article, a low magnification microscope was used to reveal the morphology and advancing motion of the film front, and the linear film growth rate at various degrees of system subcooling from the phase-equilibrium temperature corresponding to the system pressure.
Abstract: Methane hydrate films, each growing along a horizontal interface between the quiescent liquid-water and methane-gas phases, were observed through a low magnification microscope to reveal the morphology and advancing motion of the film front, and the linear film growth rate (advancing speed of the film front) at various degrees of system subcooling from the phase-equilibrium temperature corresponding to the system pressure was quantitatively measured. At a lower subcooling (≈ 1.2 K), the film front was often covered by laterally aligned facets showing a regular roughness with sharp peaks and valleys and a non-isotropic growth. As the subcooling increased, the film front tended to have an irregular, non-faceted, smaller-scale roughness and exhibited a smoother, isotropic growth. For such an isotropic, quasi-steady film growth at subcoolings from ∼2.5 to ∼10 K, we collected the film-growth rate data. The obtained data were compared to other relevant data or empirical correlations previously reported by different research groups. The consistency or inconsistency between the different data sources were examined in detail.
23 citations
TL;DR: In this article, the crystal structure of Yb: LuPO4 crystals at room temperature was refined by using single crystal X-ray diffraction data, and the results showed that the absorption spectral region was well matched for pumping with readily available diode lasers.
Abstract: Yb: LuPO4 crystals with the size up to 6×2×0.5mm3 were grown by the flux growth process using lead pyrophosphate Pb2P2O7 as the high-temperature solvent. The crystal structure of Yb: LuPO4 crystals at room temperature was refined by using single crystal X-ray diffraction data. Crystal structure analysis showed that Yb: LuPO4 crystals possessed the tetragonal xenotime structure. The polarized absorption spectra of Yb: LuPO4 were tested at room temperature. The results showed that the absorption spectral region of Yb: LuPO4 crystal was well matched for pumping with readily available diode lasers.
22 citations
TL;DR: In this paper, a self-sacrifice template was used to synthesize Urchin-like tungsten oxide hydrate (WO3·H2O) hollow spheres with typical diameters of 4-6 μm with nanoflakes of several nanometers at surface.
Abstract: Urchin-like tungsten oxide hydrate (WO3·H2O) hollow spheres were successfully synthesized via a self-sacrifice template method at low temperature. The effects of reaction parameters on the preparation were studied in solution. The growth mechanism was also proposed on the basis of experimental results. In addition, the acid amount and temperature have important effects on size control of the as-obtained samples. The achieved nanoarchitectures have typical diameters of 4–6 μm with nanoflakes of several nanometers at surface. Crystal structure, morphology, and composition of final nanostructures were characterized by X–ray diffraction (XRD) and scanning electron microscopy (SEM). Degradation experiments of organic contaminant were also performed on samples of hollow spheres and walnut-like structures under visible-light illumination. Hollow sphere sample exhibited better photocatalytic capability than walnut-like sample. Possible mechanism was studied for WO3·H2O assisted photocatalytic degradation of organic contaminant under visible light.
22 citations
TL;DR: A general overview of the biomineralization process is presented in this article, paying attention to what occurs at the interface and at the forces involved in the adsorption phenomena, with the aim to illustrate the variety of strategies that nature can adopt to form mineral structure with unique chemical and physical properties and so far not obtainable by abiotic processes under ambient conditions.
Abstract: The processes by which organisms deposit a mineral phase imply always the existence of an organic interface, does not matter the degree of control exerted. Thus adsorption phenomena, chemical and/or physical, are pivotal in the understanding of biomineralization processes. In this paper a general overview of the biomineralization is presented, paying attention to what occurs at the interface and at the forces involved in the adsorption phenomena. Several case of studies are presented with the aim to illustrate the variety of strategies that nature can adopt to form mineral structure with unique chemical and physical properties and so far not obtainable by abiotic processes under ambient conditions.
21 citations
TL;DR: In this paper, the material synthesis and the melt growth of tin monosulfide (SnS) by using the Bridgman-Stockbarger technique have been investigated.
Abstract: SnS is a promising candidate as PV absorber material according to the material properties and the Loferski diagram, but despite the numerous publications on this material, the intrinsic material properties are widely unknown and the theoretical possible values for efficiency are still far away from those achieved in reality. Due to the fact that this material is mostly grown as thin film material, bulk research is rare. The material synthesis and the melt growth of tin monosulfide (SnS) by using Bridgman-Stockbarger technique have been investigated in this study. After first growth experiments produced polycrystalline SnS, a significant reduction of the growth velocity lead to samples with a high amount of single crystalline material. These samples were investigated in detail regarding the structural and optical properties by using XRD/HRXRD, chemical etching and photoluminescence.
21 citations
TL;DR: In this paper, it is shown that the structure of sputtered Sb-Te films with various compositions between the two compounds at both ends formed in a non-thermal equilibrium showed smaller γ values, than those expected from their compositions without exception.
Abstract: It is well known that the Sb–Te binary system has a large number of incommensurately or commensurately modulated structures between Sb and Sb2Te3 compounds. These structures, which are long-period trigonal stacking structures, possess their own modulation period γ, according to their composition in the thermal equilibrium. However, the structure of sputtered Sb–Te films with various compositions between the two compounds at both ends formed in a non-thermal equilibrium showed smaller γ values, than those expected from their compositions without exception. A smaller γ value implies that its structure is closer to that of Sb with the shortest period in all Sb–Te modulated structures. With increase in temperature, all these transient structures with smaller γ, however, became stable, accompanying an increase of γ to acquire their original modulated structures.
TL;DR: In this article, the X-ray Bond method was used to carry out very precise measurements of the lattice parameters and fine correlations between values of lattice parameter and the Sr concentration in the solid solution of single crystals were found.
Abstract: Changes of lattice parameters of SrxBa1‒xNb2O6 (0.35 < x < 0.72) solid solution single crystals were measured as a function of temperature. The X-ray Bond’ method was used to carry out very precise measurements of the lattice parameters. Fine correlations between values of the lattice parameter and the Sr concentration in the solid solution of SrxBa1‒xNb2O6 single crystals are found. A conventional analysis of lattice parameter data in terms of spontaneous strain and strain/order parameter coupling shows that a normal structural phase transition does occur. While the ferroelectric system (SBN26) displays a nearly tricritical behavior, β ≈ 0.20, the relaxor one (SBN61) complies with the two-dimensional Ising-model-like criticality, β ≈ 0.17.
TL;DR: In this paper, a bloom-like ZnO nanostructures assembled by nanorods with bimodal size distribution have been synthesized by a solvothermal process in NaOH-Et system.
Abstract: Flower-like ZnO nanostructures assembled by nanorods with bimodal size distribution have been synthesized by a solvothermal process in NaOH-Et system. Various effects of the solvothermal parameters and assistant additives on the morphologies of ZnO nanostructures have been investigated. The directing effect of chloride ions have been observed in the formation of highly symmetrical 3D ZnO nanostructures. A possible mechanism has been proposed to explain the formation of ZnO nanoflowers in NaOH-Et system. A strong near-UV emission band centered at around 396 nm is observed in the photoluminescence spectrum of flower-like ZnO nanostructures, indicating of their high crystal quality.
TL;DR: In this article, the growth of lead free piezoelectric single crystals of NbO3 (K 0.5Na0.5) were compared with B2O3 flux.
Abstract: Lead free piezoelectric single crystals of sodium potassium niobate (K0.5Na0.5)NbO3 (KNN) were grown by high-temperature solution method using two different fluxes; one with a mixture of NaF and KF and other with addition of B2O3 along with the mixture. In the present study, the growth of KNN crystals without B2O3 flux and the same with B2O3 flux were compared. It was found that additions of small amounts of B2O3 lowered the melting temperature of the solid solution and enabled better dielectric properties. Phase analysis showed that all samples were crystallized in pure orthorhombic perovskite phase. AFM morphological studies showed that the addition of B2O3 flux increased the roughness of the grown crystal. Further, addition of B2O3 flux slightly decreased the orthorhombic to tetragonal phase transition temperature T(O—T) and the Curie temperature TC. The ferroelectric behaviour of KNN single crystal has been investigated at room temperature. The crystal grown using B2O3 flux exhibited a remanent polarization (Pr) ∼ 32 μC/cm2 and coercive field (Ec) of ∼11.8 kV/cm whereas the crystal grown without the use of B2O3 flux had a remanent polarization (Pr) ∼ 36 μC/cm2 and coercive field (Ec) of ∼14.6 kV/cm.
TL;DR: In this article, a case study of adsorption/absorption in growing calcite is presented, where the impurity is adsorbed and incorporated in a growing crystal, giving rise to a bi-phased system: the host dominant crystal and the guest impurity crystallized as thin lamellae in selected growth sectors.
Abstract: The paper deals with the peculiar case of adsorption/absorption in which the impurity is adsorbed and, successively, incorporated in a growing crystal, giving rise to a bi-phased system: the host dominant crystal and the guest impurity crystallized as thin lamellae in selected growth sectors. The historical path is revisited, since the pioneering papers by Johnsen, Gaubert, Neuhaus and Seifert, through the works of Kern's and Hartman's Schools who verified the theoretical hypotheses on the growth mechanisms, initially put forward by Bunn, Royer and Kleber. An important attention is paid to the interesting case study represented by the system NaCl/CdCl2, both for the pure adsorption of CdCl2 on the NaCl crystal faces and for the formation of a three dimensional mixed salt of composition CdCl2·2 NaCl·3H2O. The core of the work is devoted to two highlighting examples of adsorption/absorption. In the first one, varying concentrations of lithium ions present as impurity in aqueous CaCO3 solutions, act as habit modifiers of the growing calcite crystals (adsorption) and, contemporarily, enter the calcite lattice in selected growth sectors, as Li2CO3 iso-oriented lamellae (absorption). All this has been proved by X-ray powder diffraction diagrams (XRPD), cathode-luminescence and atomic force microscopy (AFM) measurements. In the second example, the well known example of habit modification of NaCl crystals growing from aqueous solution in the presence of formamide is recovered and newly investigated in the light of up to date experimental and theoretical analyses. NaCl crystals were obtained from water-formamide (H-CO-NH2) solutions, either by slow evaporation or by programmed cooling of saturated solutions, the formamide concentration ranging from 0 to 100%. Accordingly, the crystal morphology changes from {100} (pure aqueous solution) to {100} + {111} (water-formamide solutions) to {111} (pure formamide solution). X-ray powder diffraction diagrams prove that formamide is not only adsorbed on the {111}NaCl octahedron but is also selectively captured within the {111} growth sectors. The 2D-lattice coincidences between the d101 layers of formamide and the NaCl – d111 ones suggest that formamide can be adsorbed as ordered epitaxial layers; further, the equivalence between the thickness of the elementary layers and indicates that formamide is allowed to be buried (absorption) in the growing crystal. Hence, one can ultimately state that formamide is not only an habit modifier of NaCl crystals, but that “anomalous NaCl/formamide mixed crystals” form, limited to the {111} NaCl growth sectors.
TL;DR: In this article, complementary experimental techniques were applied to characterize bioapatite nanocrystals from pathological cardiovascular deposits, including the leaflets from aortic valve, mitral valve, tricuspid valve and calcified aorta's wall.
Abstract: Complementary experimental techniques were applied to characterize bioapatite nanocrystals from pathological cardiovascular deposits. The investigated collection included the leaflets from aortic valve, leaflets from mitral valve, leaflets from tricuspid valve and calcified aorta's wall. XRD, EDX and FTIR data have shown that all studied samples consist of imperfect apatite with different crystallinity and variable chemical composition. In accordance with TEM data, the crystals of pathological calcified deposits frequently have oblong or rod-like shape (length of 60-90 nanometers, width of 20-30 nanometers). At the same time, in the SEM and TEM experiments, the complex spheroid assemblies and planar sheet-like shaped formations with crystal structure close to apatite were observed. Probably, the different shape and morphology of the particles are caused by different ways of crystal nucleation and growth, although the exact mechanisms remain an open question.
TL;DR: In this article, the crystal phase competition was used to study the crystallization behavior and glass forming ability of Cu64Zr36 bulk metallic glass (BMG) and found that it is the competing phase Cu10Zr7 that weakens GFA.
Abstract: In the present paper, crystallization behavior and glass forming ability (GFA) of Cu64Zr36 bulk metallic glass (BMG) were studied based on the crystal phase competition. Electrical resistivity and X-ray diffraction results indicate that Cu64Zr36 glass underwent a two-stage crystallization process, during which Cu10Zr7 and Cu51Zr14 crystals precipitate at first and then there are only Cu10Zr7 and Cu8Zr3 phases at the end of the second stage. Intriguingly, it was found that it is the competing phase Cu10Zr7 that weakens GFA of the Cu64Zr36 alloy, because the Cu10Zr7 precipitate is fully restrained in the cast rod when substituting Zr with 7.5at%Ti and thereby its diameter with fully amorphous structure is enlarged from 1 mm to 2 mm.
TL;DR: In this paper, surface tension of molten silver and iron is measured and the maximum surface tension appears at a certain temperature, below which temperature coefficient of surface tension is positive, due to change of temperature coefficient, Marangoni flow direction shows variation in a liquid bridge configuration.
Abstract: Measurements of surface tension of molten silver and iron are reviewed. Surface tension of molten silver and iron show boomerang-shaped behavior; the maximum surface tension appears at a certain temperature, below which temperature coefficient of surface tension is positive. Due to change of temperature coefficient, Marangoni flow direction shows variation in a liquid bridge configuration.
TL;DR: ZnO/SrTiO3 core/shell nanorod arrays were fabricated by a facile two-step method as discussed by the authors, where ZnO was first hydrothermally grown on Si substrate.
Abstract: ZnO/SrTiO3 core/shell nanorod arrays were fabricated by a facile two-step method. ZnO nanorod arrays were first hydrothermally grown on Si substrate. Then, using liquid phase deposition method, SrTiO3 were deposited onto the ZnO nanorods to form core/shell nanorod structures. The morphologies and structures of the products were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The photocatalytic behavior of the nanorod arrays was also examined through the photodegradation of methylene blue solution under UV irradiation. It was found that the core/shell nanorod arrays with deposition time of 10 min showed higher photocatalytic activity than bare ZnO nanorod arrays. This enhancement was attributed to the efficient charge separation at the ZnO/SrTiO3 interface.
TL;DR: The Coulomb-London-Pauli model is reviewed in this paper and its incorporation into empirical or semi-empirical force fields is described in comparison with ab initio quantum chemical computation.
Abstract: The physical principles of chemical bonding are reviewed in the Feynman perspective. The Coulomb-London-Pauli model, which separates intermolecular interaction into Coulombic, dispersion and repulsion terms, is reviewed and its incorporation into empirical or semi-empirical force fields is described in comparison with ab initio quantum chemical computation. Quantitative assessments of pair-wise intermolecular coupling energies are presented, and orders of magnitude are established for several types of crystal construction. The wide energetic separation between dispersive and ionic aggregation is quantitatively evaluated. Molecular dynamics (MD) and Monte Carlo (MC) simulation techniques are succinctly described. Key problems in molecular-level pictures of crystal nucleation and growth are outlined, and possible applications of evolutionary (MC or MD) simulation are introduced and discussed. More generally, the significance and value of molecular simulation is criticized. A final section deals with the related phenomenon of crystal polymorphism, with its underpinnings in the kinetics of nucleation versus thermodynamics of crystal stability.
TL;DR: In this paper, the solubility data of HMX (1,3,5,7-tetranitro-1, 3, 5, 7tetrazocane) was accurately measured by use of the laser-monitoring observation technique, and the growth rate and nucleation rate at different conditions were calculated according to these equations.
Abstract: In this paper, the solubility data of HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) in acetone from 323.15 K to 293.15 K were accurately measured by use of the laser-monitoring observation technique. Intermittent dynamic method was utilized to study crystallization kinetics of HMX in acetone. The data of crystallization kinetics were obtained by moment analysis, and the parameters of the growth rate and nucleation rate equations were derived by using multiple linear least squares method. Subsequently, growth rate and nucleation rate at different conditions were calculated according to these equations. In addition, Optical Microscopy Images (qualitative) and Particle Apparent Density (quantitative) experiments were applied to study the crystal internal defects of HMX under different crystallization conditions. It can be found that the crystal apparent density of HMX is in the range of 1.8993 g·cm−3 to 1.9017 g·cm−3, very close to the theory density of HMX; the internal defects and the crystal size do not increase after 25 °C, from which we predict that the HMX crystal growth reaches the steady growth segment. These results suggest that the nucleation rate is a significant factor influencing the crystal internal defects, and larger nucleation kinetics can reduce crystal internal defects.
TL;DR: In this paper, a two-step post grown annealing method aimed at reduction of Te inclusions while keeping the resistivity high is presented, where the influence of the Fermi level on electron trapping and recombination is summarized.
Abstract: We present results of development of CdZnTe semi-insulating crystals prepared by Vertical Gradient Freeze method in a 4-zone furnace. We applied the way of growth of the crystal from the top when the first crystallization seed is created on the surface of the melt. The typical height of the crystals is 5 cm. Resistivity and photoconductivity profiles measured along the growth axis by contactless method are compared and their mutual correlation is explained based on a model of relative shift of the Fermi level and the midgap level present in the material. The influence of the Fermi level on electron trapping and recombination is summarized. We present here results of a two-step annealing method aimed at reduction of Te inclusions while keeping the resistivity high. We employed CdTe:Cl VGF grown samples to eliminate Te inclusions observed in as grown crystals by two-step post grown annealing in Cd and Te atmosphere and present a model of the processes leading to high resistivity material after annealing.
TL;DR: In this article, the state-of-the-art for double salt iodide scintillators, in particular cesium barium iodide (CBI), CCI, and barium bromine iodide(BBI), were reviewed.
Abstract: In this study we review the state-of-the-art for double salt iodide scintillators, in particular cesium barium iodide (CBI), cesium calcium iodide (CCI) and barium bromine iodide (BBI), as well as report on their scintillation and optical properties. Double salt iodides inherently have high density and atomic number which translates to good stopping power for energetic particles, in particular gamma rays. Light yields of 54,000 ph/MeV for CBI, 51,000 ph/MeV for CCI, and 46,000 ph/MeV for BBI were measured. A FWHM energy resolution for the 662 keV full absorption peak was observed at 5.7% for CBI, 16.3% for CCI and 3.56% for BBI. The principal scintillation decay timing for CBI was 840 ns, 462 ns for BBI, and two distinct time components of 9 ns and 1900 ns were observed for CCI.
TL;DR: In this paper, the influence of the growth temperature on the morphology and microstructure of the ZnO nanorods was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD).
Abstract: ZnO nanorod arrays have been successfully prepared on ITO substrate by a chemical-bath deposition method at different growth temperatures. The influence of the growth temperature on the morphology and microstructure of the ZnO nanorods was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the diameter of the ZnO nanorods decreased and the size of the nanocrystals increased with increasing growth temperature. Optical absorption measurements showed the absorption band edge has shifted to a lower-energy region due to the quantum size effect. Green emission and UV emission bands were observed and they are found to be temperature dependent, which indicates that the deep-level emission and band-edge emission of ZnO nanorods is closely related to the rod diameter, and the related mechanism is discussed.
TL;DR: In this paper, suitable TiO2 nanoparticles were successfully synthesized by sol-gel method, in order to utilize the freshly prepared TiO 2 nanoparticles for proton exchange membrane (PEM) preparation.
Abstract: In the present paper, suitable TiO2 nanoparticles are successfully synthesized by sol-gel method, in order to utilize the freshly prepared TiO2 nanoparticles for proton exchange membrane (PEM) preparation. Titanium tetrachloride (TiCl4) is used as precursor and ethanol as a solvent. The optimum and suitable TiO2 nanoparticles were obtained by varying gelatinisation time (4–120 h), concentration of precursor (TiCl4) in ethanol (2–15 vol%), and reaction temperature (15–35 °C). The morphology, size and purity of the nanoparticles are investigated by transmission electron microscope (TEM), dynamic light scattering (DLS) and X-ray diffraction (XRD). Optimum results were found at 4 h of gelatinisation time, 10% precursor concentration and 25 °C temperature for preparation of TiO2 nanoparticles. Thus prepared nanoparticles are found to be suitable for preparation of nanocomposite PEM, and consequently the prepared PEM indicates enhanced properties, such as, higher thermal stability (high glass transition temperature of 184.1 °C), excellent proton conductivity (0.0822 S cm−1 at room temperature) and low methanol permeability (1.11 × 10−9 cm2 s−1).
TL;DR: In this paper, a brief review of crystal dipolar surfaces and the way to stabilize them are discussed, and the importance of taking into account the bulk symmetry of the crystal when a surface reconstruction is performed is discussed.
Abstract: In this brief review the crystal dipolar surfaces and the way to stabilize them are discussed Two classes of crystals are interested: intrinsically polar crystals and non-polar crystals, where the polarity along some directions is the consequence of the alternating layers of positive and negative charges I discuss the importance of taking into account the bulk symmetry of the crystal when a surface reconstruction is performed As examples, different reconstructions of the {111} form of halite (NaCl), and the {012} and {001} forms of calcite (CaCO3) are discussed in detail
TL;DR: In this article, the room temperature epitaxial growth of CeO2 on lattice matched (001) LaAlO3 substrates by using pulsed laser deposition (PLD) method under various oxygen partial pressure (Po2) is demonstrated.
Abstract: The room temperature epitaxial growth of CeO2 on lattice matched (001) LaAlO3 substrates by using pulsed laser deposition (PLD) method under various oxygen partial pressure (Po2) is demonstrated. X-ray diffraction analysis with 2-Theta/rocking curve/Phi-scan, cross-sectional transmission electron microscopy with selected-area diffractions are used to characterize structural of grown films. The epitaxial (001) CeO2 can be achieved at room temperature under Po2 less than 2 × 10−3 Torr. The best quality of grown film is obtained under Po2 = 2 × 10−5 Torr and degraded under Po2 = 2 × 10−6 Torr due to oxygen deficiency in structure. The epitaxial relationship between CeO2 and LAO is confirmed to be (001)CeO2 //(001)LAO, [100]CeO2//[110]LAO and [010]CeO2//[10]LAO. No obvious reduction reaction occurred, from Ce+4 turned into Ce+3 states, as reducing oxygen partial pressure during growth by PLD.
TL;DR: In this paper, the effect of Tm3+ on the spectroscopic properties upon excitation of an 800 nm laser diode has been investigated by growing LiYF4 single crystals by a Bridgman method.
Abstract: High quality Er3+/Tm3+:LiYF4 single crystals were grown by a Bridgman method. The absorption spectra and luminescent properties of the crystals were studied to characterize the effect of Tm3+ on the spectroscopic properties upon excitation of an 800 nm laser diode. The broaden 1.5 μm and the enhanced 2.7 μm emission were observed in the Er3+/Tm3+ co-doped LiYF4 single crystals. Meanwhile, the up-conversion and 1.5 μm emission intensities from Er3+ decrease with increasing the ratio of Tm3+ to Er3+. The energy transfer processes between Tm3+ and Er3+ in the Er3+/Tm3+ co-doped samples were analyzed. The energy transfer efficiency ηETE from Er3+ to Tm3+ is calculated. The highest ηETE of 65.30% for the sample with 0.296 mol% of Er3+, 0.496 mol% of Tm3+ concentration was obtained. The present work indicates that Er3+/Tm3+ co-doped LiYF4 single crystal can be a promising material for the potential application in infrared devices.
TL;DR: An all-inclusive review on the adsorption-absorption phenomena concerning both equilibrium and growth of crystals is presented in this paper, where a logical path starts with the relations between the adorption and the growth of pure crystals, continues with the change of the crystal shape due to the surface adsoption of foreign substances (without absorption in the crystal bulk) and terminates with the absorption and crystal growth.
Abstract: An all-inclusive review is proposed on the adsorption-absorption phenomena concerning both equilibrium and growth of crystals. The logical path starts with the relations between the adsorption and growth of pure crystals, continues with the change of the crystal shape due to the surface adsorption of foreign substances (without absorption in the crystal bulk) and terminates with the absorption and crystal growth. Historical aspects are widely illustrated along with the fascinating alternation of observations, experimental efforts and theoretical knowledge.
TL;DR: In this article, a 3-dimensional 3-D dandelion-like Sb2S3 nanostructures consisted of numerous nanorods have been achieved via a facile citric acid-assisted solvothermal process.
Abstract: Well-defined (three-dimensional) 3-D dandelion-like Sb2S3 nanostructures consisted of numerous nanorods have been achieved via a facile citric acid-assisted solvothermal process. The as-prepared products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), respectively. The influence factors of the formation of the hierarchical Sb2S3 nanostructures are discussed in details based on FESEM characterizations. By simply controlling the quantity of citric acid, the nucleation and growth process can be readily tuned, which brings the different morphologies and nanostructures of the final products. On the basis of a series of contrastive experiments, the aggregation-based process and anisotropic growth mechanism are reasonably proposed to understand the formation mechanism of Sb2S3 hierarchical architectures with distinctive morphologies including nanorods, and dandelion-like nanostructures. Charge-discharge curves of the obtained Sb2S3 nanostructures were measured to investigate their electrochemical hydrogen storage behaviors. It revealed that the morphology played a key role on the hydrogen storage capacity of Sb2S3 nanostructure. The dandelion-like Sb2S3 nanostructures exhibited higher hydrogen storage capacity (108 mAh g−1) than that of Sb2S3 nanorods (95 mAh g−1) at room temperature.