Synthesis and tribological properties of Mo‐doped WSe2 Nanolamellars

The Mo‐doped WSe₂ nanolamellars have been successfully prepared via solid‐state thermal (750 °C) reaction between micro‐sized W, Mo with Se powders under inert atmosphere in a closed reactor and characterized by X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the morphologies of the as‐prepared products changed from microplates to nanolamellars to aggregations composed of nanoparticles with the doping of Mo powders. And the sizes of crystallites evidently reduced while the contents of dopant increased within a certain limit (1 wt.%–7 wt.%). The tribological properties of the as‐prepared products as additives in HVI750 base oil were investigated by UMT‐2 multispecimen tribotester. The friction coefficient of the base oil containing Mo‐doped WSe₂ nanolamellars was lower and more stable than that of WSe₂ nanolamellars. A combination of rolling friction, sliding friction, and stable tribofilm on the rubbing surface could further explain the good friction and wear properties of Mo‐WSe₂ nanoparticles as additives than that of WSe₂.     

Synthesis and tribological properties of NbSe3 nanofibers and NbSe2 microsheets

NbSe₃ nanofibers and NbSe₂ sheets were prepared by solid state reaction. The as‐prepared products are characterized by powder X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the obtained NbSe₃ nanofibers have a diameter in the range of 100–300 nm and length about 10 μm, while the NbSe₂ sheets have a hexagon structure. The tribological properties of the as‐prepared NbSe_x powders as additives in HVI500 base oil were investigated on UMT‐2 multispecimen tribo‐tester. The wear scars were measured by VEECO WYKO NT1100 non‐contact optical profile testing instrument. It is found that the addition of both NbSe_x nanofibers/sheets improves the tribological properties of base oil. Furthermore, NbSe₂ sheets exhibit better friction reduction and wear resistance properties than NbSe₃ nanofibers in HVI500 base oil. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tribological properties of WSe2 nanorods as additives

This work demonstrats a convenient and effective approach to synthesize WSe₂ nanorods at only 600 °C in argon atmosphere after ball milling. The friction and wear properties of WSe₂ nanorods as additives in two kinds of base oil, GyT130 oil and 60N oil were systematically investigated. Compared to base oil, the friction coefficient of the base oil containing WSe₂ nanorods was obviously reduced and the wear behaviour was improved. The nanorods in the 60N base oil showed better tribological properties than that in the GYT130 oil. The friction‐and‐wear mechanism of the WSe₂ nanorods as lubrication additive was discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and tribological properties of hexagonal titanium silicon carbide crystals

Hexagonal titanium silicon carbide (Ti₃SiC₂) crystals were prepared by vacuum sintering of Ti, Si, and C powders at 1300 °C. The microstructure and grain deformations of Ti₃SiC₂ were examined by scanning electron microscopy and transmission electron microscopy. The tribological properties of hexagonal Ti₃SiC₂ crystals as lubrication additive in HVI500 base oil were investigated by a UMT‐2 ball‐on‐plate friction and wear tester. The Ti₃SiC₂ additives exhibited good friction reduction. Under determinate conditions, the friction coefficient of base oil containing Ti₃SiC₂ crystals is lower than that of pure base oil. The base oil with 3.0 wt.% hexagonal Ti₃SiC₂ crystals presented good anti‐wear capability. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and tribological properties of copper matrix solid self‐lubricant composites reinforced with NbSe2 nanoparticles

Copper matrix solid self‐lubricant composites were prepared by powder metallurgy route using copper powders and NbSe₂ nanofiber or sheet. The tribological properties of the as‐prepared materials were estimated by a ball‐on‐disc on UMT‐2 multi‐function friction and wear tester under dry conditions in a normal laboratory atmosphere (55‐70% relative humidity, 15‐25 °C). The NbSe₂ nanofiber or sheet was very effective in improving the tribological properties of the composites. It is found that the composites with 15 wt.% NbSe₂ nanofibers showed a very low coefficient of friction of 0.1487. Furthermore, the value levels of electrical resistivity for the composites with different contents of NbSe₂ nanofiber reached to 10^‐6 Ω.cm. When the NbSe₂ content was high enough, a continuous supply of NbSe₂ nanofiber to the tribo‐surface is an important precondition and the benefit of its anti‐friction properties for the copper matrix composites. This behavior is related that little NbSe₂ is reacted with the Cu‐base in the sintering process, although there needs enough NbSe₂ nanofibers as solid lubricants; too much NbSe₂ nanofibers will decrease the intensity of the composites, reducing the wear resistance. So adding the appropriate contents of NbSe₂ nanofiber to the composites play an important role in anti‐friction and wear resistance. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,characterization, and tribological properties of two‐dimensional Ti3C2

We report on the preparation of two‐dimensional (2D) Ti₃C₂ and its friction and wear properties. Laminated Ti₃AlC₂ was synthesized by pressureless sintering using Ti, Al, and graphite, followed by HF exfoliation and sonication treatment to form 2D‐layered Ti₃C₂, which exhibited individual layer or stack of several layers. Analysis of microstructure and composition was used to confirm the successful exfoliation of laminated Ti₃AlC₂. The tribological behaviors of the as‐prepared 2D Ti₃C₂ as a lubrication additive in base oil were investigated. Results indicate that 2D‐layered Ti₃C₂ can greatly enhance the friction‐reducing and anti‐friction properties of base oil, especially with 1.0 wt% Ti₃C₂. This novel 2D‐layered Ti₃C₂ would be a good candidate for lubricating materials to meet emerging needs in practical applications.     

Synthesis and tribological properties of laminated Ti3SiC2 crystals

Laminated Ti₃SiC₂ crystals are prepared of Ti, Si, C and Al powders by the method of hot isostatic pressing with NaCl additive in argon at 1350 °C. The laminated morphology of Ti₃SiC₂ is presented through the SEM and TEM observations. The results of high resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED) patterns combined, it can be seen that the layers are of Ti₃SiC₂ crystals. The growth mechanism of Ti₃SiC₂ crystals, controlled by two‐dimensional nucleation, is also explained. The tribological properties of Ti₃SiC₂ crystals as additives in HVI500 base oil are investigated by a UMT‐2 ball‐on‐plate friction and wear tester. The study shows that under determinate conditions, the friction coefficient of the base oil containing Ti₃SiC₂ crystals is lower than that of pure base oil, and it decreases with the increase of mass percent of Ti₃SiC₂ nanolayers when its proportion is lower than 5wt. %. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multi‐factors on photocatalytic properties of Y‐doped Bi2WO6 crystallites prepared by microwave‐hydrothermal method

Different contents of Y‐doped Bi₂WO₆ crystallites were synthesized by a microwave‐hydrothermal method. The photocatalytic properties with different contents of Y‐doped Bi₂WO₆ crystallites were studied. The Y‐doped Bi₂WO₆ crystallites were also characterized by XRD, EDX, SEM and UV‐vis DRS and the multi‐factors on photocatalytic properties of Y‐Doped Bi₂WO₆ crystallites were discussed. The results indicate that Y³⁺ replacing Bi³⁺ enters into the Bi₂WO₆ lattice, producing a degree of Bi₂WO₆ lattice distortion. It also has an impact on the crystallinity of Bi₂WO₆ and the band gap is from 2.49 eV to 2.71 eV. The photocatalytic results show that when the content of Y doping becomes 10%, the degradation rate of rhodamine B is above 90% after 40 min irradiation, which shows that doping the proper rare earth ions is conducive to the photocatalytic properties of Bi₂WO₆ crystallites.     

Crystal growth of zirconium‐doped KTiOPO4 crystals in the K2O‐P2O5‐TiO2‐ZrF4 system

Zirconium‐doped KTiOPO₄ (KTP) crystals were grown using a high temperature flux method in the K₂O‐P₂O₅‐TiO₂‐ZrF₄ system. The dopant content in the single crystals with general composition KTi_1‐xZr_xOPO₄ (where x = 0 – 0.026) strongly depends on zirconium concentration in the homogeneous melts. AES‐ICP method and X‐ray fluorescence analysis were used to determine the composition of the obtained crystals. Phase analyses of the products were performed using the powder XRD. The structures of KTiOPO₄ containing different quantities of Zr were refined on the basis of single crystal XRD data. Applying ZrF₄ precursor for zirconium injection into the flux allowed growing the zirconium‐doped KTP crystals at 930–750°C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lithium Intercalation into the Tetradymite-type Selenides Sulfides Bi2Se3-xSx

The reaction rate of Li intercalation into Bi₂Se_3−xS_x single crystals (x = 0, 0.025 and 0.05) increases with an increasing sulfur content in the crystals. This effect has been explained qualitatively by a change in the bond polarity in the Bi₂Se₃ due to the substitution of selenium atoms by sulfur atoms. This substitution results in a change in the electron density distribution and thus also in the width of the van der Waals gap between the structural layers, responsible for the course of intercalation. This explanation is supported by a quantum-chemical calculation of the charges on the atoms of the Bi₂Se_3−xS_x lattice manifesting and increase in the negative charge on Se atoms with an increasing value of x.     

Synthesis and optical properties of CuInS2 thin films prepared by sulfurization of electrodeposited Cu‐In layers

The chalcopyrite CuInS₂ thin film was fabricated at 500 °C for 2 h by sulfurization of Cu‐In layers (as precursors) that were sulfurized in a glass tube with pure sulfur powder. The structural, morphological, and optical properties of CuInS₂ thin films are characterized using X‐ray diffraction (XRD), field‐emission scanning electron microscope (FE‐SEM), and UV/Visible/NIR spectrophotometer. The study of UV/Visible/NIR absorption shows the band gap energy value of CuInS₂ thin films is 1.5 eV. The XRD pattern shows the film is pure CuInS₂; no other peaks, such as CuS or CuIn₅S₈ were observed. Furthermore, the surface of the CuInS₂ film is compact characterized by FE‐SEM, which also shows the disappearance of CuS on the surface at 500 °C.     

Effects in B–doped KDP crystals irradiated with neutrons of large spectra energy

The results obtained for the r₆₃ electro‐optic coefficient of B‐doped and undoped KDP (KH₂PO₄) crystals irradiated with neutrons (including thermalized neutrons) produced by scattering of 30 Mev cyclotron protons on a target of Ta²⁰¹, are presented and compared to those obtained for non‐irradiated doped and undoped crystals. The B‐doped (H₃BO₃, Na₂B₄O₇ and Li₂B₄O₇) crystals were obtained by the conventional growth method by temperature decrease with 1 wt % dopant concentration in solution. The thermal neutron flux was around ϕ = 1. 10¹⁰ n/cm² s. Pulses of ∼15 μs long, in damped oscillatory mode (V= 8 kV, τ=1.95 μs) were used for the electro‐optic measurements. A Pockels cell, a photomultiplier, a He‐Ne laser (λ=632.8 nm, 5 mW, linearly polarized) and a Tk 720 A oscilloscope complete the experimental setup. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zr‐doped CeO2 Hollow slightly‐truncated nano‐octahedrons: One‐pot synthesis,characterization and their application in catalysis of CO oxidation

Zirconium‐doped ceria hollow slightly‐truncated nano‐octahedrons (HTNOs) (Ce_1‐xZr_xO₂) were synthesized by a one‐pot, facile hydrothermal method. The morphology and crystalline structure were characterized with powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and the high resolution transmission electron microscopy (HRTEM). The composition and chemical valence on the surface of the as‐prepared Ce_1‐xZr_xO₂ powders were detected by X‐ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS). The surface area and pore size distribution of as‐obtained Zr‐doped ceria HTNOs were measured by N₂ adsorption‐desorption measurement. Mechanisms for the growth of Zr‐doped ceria HTNOs are proposed as both oriented attachment and Ostwald ripening process and the formation of the hollow structure is strongly dependent on the addition of Zr⁴⁺ ions. Furthermore, the as‐obtained Zr‐doped ceria HTNOs revealed superior catalytic activity and thermal stability toward CO oxidation compared to pure ceria. It may provide a new path for the fabrication of inorganic hollow structures on introducing alien metal ions.     

Structural,optical, electrical and luminescence properties of electron beam evaporated CdSe:In films

CdSe:In films were prepared by electron beam evaporation technique using CdSe and In₂Se₃ (purity ∼99.9%) pellets. The crystal structure of the films with and without Indium, measured by X‐ray diffraction (XRD), showed a typical wurtzite structure, higher Indium doping shifts the peak angle to higher side along with the broadening of the peaks. X‐ray photoelectron spectroscopy (XPS) studies indicated binding energies corresponding to 54 eV (Se3d_5/2), 444 eV (In 3d_5/2), 411 eV (Cd 3d_3/2), (Cd 3d_5/2). Atomic force microscope (AFM) studies indicated a uniform surface.The grain size decreases with increase of In doping. A decrease in the band gap was observed with increase of dopant concentration. Resistivity of the films is in the range of 10^‐3 Ωcm. Carrier density was in the range of 10²¹ cm^‐3 for the films. The photolumineasenec spectra (PL) spectra indicated three peaks. The peak intensity decreases as the Indium concentration increases. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Local structure of liquid Rb–Se mixtures near the miscibility gap

In the liquid Rb–Se mixture there exists a liquid–liquid phase separation (miscibility gap) in the Se-rich concentration region. In order to study how the local structure is associated with the occurrence of the miscibility gap, EXAFS and neutron diffraction measurements for liquid Se, Rb₁₀Se₉₀, Rb₁₅Se₈₅ and Rb₂₀Se₈₀ mixtures have been carried out. The results reveal that the interaction between Rb and Se atoms is very weak and the liquid mixtures are composed of short Se chain-molecules of which chain ends are terminated by Rb atoms. We have carried out detailed structural modeling studies using reverse Monte Carlo simulation. It is found that the chain-like or ring-like Se segments are separated by voids. The Rb atoms adsorbed to Se chain ends segregate in the void and the shortened Se chain-molecules link up with each other when one approaches the miscibility gap.     

Crystal structure of 2‐(3‐amino‐2,4,4‐tricyano‐buta‐1,3‐dienyl)‐ thiophene

The title compound (C₁₁H₆N₄S) crystallizes in the orthorhombic space group Pbca with a = 23.561(4) Å, b = 7.064(1) Å, c = 13.018(3) Å, Z = 8; D_x = 1.387(1) g.cm^‐3 ; R = 0.073 for 1697 observed reflections [F2 ≥ 2σ(F²)]. The interesting feature is disorder in the crystal structure resulting from the existence of two isomeric molecules with interchangable carbon and sulfur positions, occuring at random but with equal probability in the structure.     

Optical Properties of Bi2Se3‐xAsx Single Crystals

Bi₂Se_3‐xAs_x single crystals with the As content of c_As = 0 to 2.0x10¹⁹ atoms/cm³ prepared from the elements of 5N purity by means of a modified Bridgman method were characterized by measurements of infrared reflectance and transmittance. Values of the plasma resonance frequency omega_p, optical relaxation time tau, and high‐frequency permittivity were determined by fitting the Drude‐Zener formulas to the reflectance spectra. It was found that the substitution of As atoms for Se atoms in the Bi₂Se₃ crystal lattice leads to a decrease in the omega_p values. This effect is accounted for by a model of point defects in the crystal lattice of Bi₂Se_3‐xAs_x. The dependences of the absorption coefficient K on the energy of incident photons were determined from the transmittance spectra. The optical width of the energy gap is found to decrease with increasing As content. The values of the exponent b from the relation of K ∼ lamda^b for the long‐wavelength absorption edge range within the interval 2.0 to 2.3, i.e. the dominant scattering mechanism of free current carriers in Bi₂Se_3‐xAs_x crystals is the scattering by acoustic phonons.     

Phase transformation in the system TlBi(Te1‐xSex)2

TlBiTe₂ and TlBiSe₂ ‐ that are ternary analogs of the IV‐VI semiconductors ‐, although they crystallize in the same space group R m (D⁵_3d), exhibit different behaviour during heating. The observed phase transformation depends on Se content (x) in the system TlBi(Te_1‐xSe_x)₂ and the transformation disappears by increasing Se content after a certain value (x = 0.25). This dependence is examined through the analysis of the DSC non‐isothermal measurements and an attempt for the explanation of the observed behaviour is undertaken through the consideration of off‐center atoms. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of polymerizing agent on structure and spectroscopic properties of nano‐crystalline La0.8Sr0.2MnO3 powders

Strontium‐doped lanthanum manganite (La_1‐xSr_xMnO₃ or LSM) is the material most widely used on solid oxide fuel cells cathode. In this work, nano‐scale La_0.8Sr_0.2MnO₃ powders have been synthesized by polymeric precursor‐based methods using different polymerizing agents with the aim of evaluating the influence of this change in the final powder. The powders calcined at 700 °C for 2 h have been characterized by X‐ray diffraction (XRD), scanning electron microscopy (FE‐SEM) and Fourier transform infrared spectroscopy (FTIR) in order to investigate the quality of both synthesis routes. It is shown that the crystal structure and morphology of the particles are significantly dependent on the preparation conditions. Single phase and La_0.8Sr_0.2MnO₃ nano‐crystalline particles less than 30 nm were obtained using ethylene glycol as polymerizing agent. FTIR results have been indicated that only the powder obtained using gelatin presented small traces of hydroxyl groups on its surface. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of annealing on structural,electrical and optical properties of AgGa(Se0.5S0.5)2 thin films deposited by using sintered stoichometric powder

The structural, electrical and optical properties of AgGa(Se_0.5S_0.5 )₂ thin films deposited by using the thermal evaporation method have been investigated as a function of annealing in the temperature range of 450–600 °C. X‐ray diffraction (XRD) analysis showed that the structural transformation from amorphous to polycrystalline structure started at 450 ^oC with mixed binary phases of Ga₂Se₃, Ga₂S₃, ternary phase of AgGaS₂ and single phase of S. The compositional analysis with the energy dispersive X‐ray analysis (EDXA) revealed that the as‐grown film has different elemental composition with the percentage values of Ag, Ga, Se and S being 5.58, 27.76, 13.84 and 52.82 % than the evaporation source powder, and the detailed information about the stoichometry and the segregation mechanisms of the constituent elements in the structure have been obtained. The optical band gap values as a function of annealing temperature were calculated as 2.68, 2.85, 2.82, 2.83, and 2.81 eV for as‐grown, annealed at 450, 500, 550, and 600 °C samples, respectively. It was determined that these changes in the band gap are related with the structural changes with annealing. The temperature dependent conductivity measurements were carried out in the temperature range of 250‐430 K for all samples. The room temperature resistivity value of as‐grown film was found to be 0.7x10⁸ (Ω‐cm) and reduced to 0.9x10⁷ (Ω‐cm) following to the annealing. From the variation of electrical conductivity as a function of the ambient temperature, the activation energies at specific temperature intervals for each sample were evaluated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)