Magnetic properties and surface morphology of layered In2Se3 crystals intercalated with cobalt

The magnetic properties of layered Co _x In₂Se₃ crystals electrochemically intercalated with cobalt in an external magnetic field and without a magnetic field and the morphology of the van der Waals surfaces of layers of these crystals have been investigated. It has been found that the ferromagnetic ordering at room temperature is observed only for Co _x In₂Se₃ crystals intercalated in an external magnetic field. These crystals are nanocomposite materials that consist of a layered matrix and arrays of nanorings and nanowires formed from Co nanocrystals on the van der Waals surfaces of the In₂Se₃ layers. Cobalt nanocrystals in Co _x In₂Se₃ crystals have a pyramidal equilibrium shape, which is characteristic of the face-centered cubic crystal structure, and their geometrical sizes are of the order of a few nanometers. The specific features of self-organization of cobalt magnetic nanostructures on the van der Waals surfaces of layered semiconductor crystals during their electrolytic intercalation in a magnetic field and the magnetic properties of these structures have been considered.     

Photoluminescent property of mechanically milled BaWO4 powder

Crystalline BaWO₄ (BWO) powder obtained by the polymeric precursor method was structurally disordered by means of high-energy mechanical milling. For the first time a strong and broad photoluminescence (PL) has been measured at room temperature for mechanically milled BWO powder and interpreted by ground-state quantum mechanical calculations in the density functional theory framework. Two periodic models have been studied; one representing the crystalline form and the other one representing the disordered BWO powder. These models allowed the calculation of electronic properties, which are consistent with the experimental results, showing that structural disorder in the lattice is an important condition to generate an intense and broad PL band.     

Electronic structure and properties of NbS2 and TiS2 low dimensional structures

Transition metal dichalcogenides have a laminar structure, weakly bound through van der Waals interactions. Due to their technological applications in catalytic processes the bulk structure of many of them has been widely studied in the last 30 years. Some of them, such as NbTe₂ and TiSe₂, show superconductivity and have been, therefore, the subject of intense study. Novoselov et al. (2005 [1]) achieved to isolate not only graphene but also other bidimensional crystals, among them layers of some dichalcogenides. These bidimensional crystals preserve their monocrystallinity under normal ambient conditions, keeping the crystal structure of the bulk. In this contribution we calculate the magnetic and electronic properties of 2D layers of NbS₂ (non-magnetic metal in 3D) and TiS₂ (non-magnetic semimetal in 3D) as well as quasi 1D chains cut out from these layers.     

Luminescence properties of BaWO4 single crystal

UV excited photoluminescence from BaWO₄ (BWO) single crystals has been investigated in the temperature range of 77-300 K. The presence of two emission bands in the UV and blue spectral regions is observed under excitation by 230 nm at room temperature. The observation of UV emission band at room temperature is a novel result. The thermal treatment at elevated temperatures under air or vacuum is observed to influence the optical and luminescence properties of the crystal. The changes brought about by annealing in air are found to be reversible. However, in vacuum annealed samples the UV emission is completely quenched.     

Structure, properties, and formation models of optical ceramics

The structure, properties, and formation mechanisms of Y₃Al₅O₁₂, Y₂O₃, and Lu₂O₃ laser ceramics are investigated. Their microhardness and fracture toughness are determined. It is shown that the change in mechanical properties is related both to the grain size and grain boundary structure. Processes of plastic deformation of crystals by mechanical twinning are considered. Mechanisms of formation and motion of twins in crystals with FCC structure are determined. It is shown that the realization of similar mechanisms in crystals with HCP structure results in the phase transformations. Models of the formation and motion of twin boundaries are proposed which result in pore healing when preparing monolithic samples of highly transparent ceramics.     

Growth and characterization of ferroelectric SrBi2Ta2O9 single crystals via high-temperature self-flux solution method

SrBi₂Ta₂O₉ (SBT) single crystals were produced by the high-temperature self-flux solution method using a Bi₂O₃ flux modified with B₂O₃. The processing conditions were optimized to obtain large and translucent SBT crystals with a layered habit and typical dimensions of approximately 7 × 5 × 0.2 mm. X-ray diffraction and x-ray topography measurements revealed that the major faces of the crystals with natural rectangular platelet morphology are perfectly (001)-oriented with edges directed along the [110] directions. The high quality of the crystals was confirmed by rocking curves (half-width of 0.04° for the (0018) reflection) and by ferroelectric measurements. The anisotropy in the dielectric and ferroelectric properties was investigated both along the [110] (ab plane) and the [001] (c axis) directions. The growth mechanism, morphology, and dielectric anisotropy of the SBT crystal platelets are discussed based on its crystallographic structure. This article was submitted by the authors in English     

The effect of molecular weight on the structure and thermal properties of polyethylene

The morphology of polyethylene single crystals prepared isothermally in solution was found to be independent of molecular weight. The enthalpy of fusion, lamellar fold period, and optical appearance were invariant for samples grown from fractions ranging from 20,000 to 2,000,000 in molecular weight. The mass fraction of lamellae which thicken during heating decreased linearly with increasing log molecular weight. The melting temperature of the crystals was also nearly independent of molecular weight.

The superheating of polyethylene crystals was observed to be a function of molecular weight and morphology. At a comparatively high molecular weight the heating rate of the calorimeter exceeded the crystal melting rate, which shifted the observed melting temperature to an anomalously high value. The incorporation of defects within the crystals by irradiation-induced cross-links or chain entanglements increased the melting rate of the high molecular weight samples and thereby minimized the effects of superheating.

The apparent heat of fusion of melt crystallized polyethylene decreased linearly with increasing log molecular weight. In contrast to this behavior the crystallinity of single crystals from dilute solution was independent of molecular weight.

In previous papers we have shown that reorganization of polymer single crystals is suppressed by cross-linking [1—3]. With the appropriate selection of heating rate and irradiation dose, the melting temperatures of solution grown crystals of various morphologies were determined in the absence of lamellar thickening. The observed melting temperatures of polyethylene single crystals with different X-ray fold periods were found to fit the following expression:

T_m = T_m0[1—2σ_e/H_f?] with an equilibrium melting temperature (T_m0) of 145.8 ± 1.0°C and a surface free energy (σ_e) of 89 ± 5 ergs cm^?2 for a polyethylene crystal of infinite dimensions. In addition, at a constant heating rate it was observed that the fraction of crystals which thickened prior to melting decreased with increasing fold period.

Since cross-linking polyethylene increases the molecular weight of the material, it is instructive to investigate the reorganization characteristics of single crystals prepared from polyethylene fractions. Single crystals were prepared in xylene from molecular weight fractions of polyethylene and the effect of molecular weight upon the structure and thermal properties of the crystals was determined.     

Study of the structural and physicochemical properties of nanostructured zirconia crystals for fabricating an innovative electrosurgical tool

To optimize the chemical composition of the crystals of nanostructured partially stabilized zirconium dioxide for fabricating cutting parts of an electrosurgical tool, the structural and strength properties of these crystals were investigated in dependence on the stabilizing impurity (Y₂O₃) content and the effect of additional dopants on the critical properties of the material was studied. It was established that in all the investigated crystals without additional doping, regardless of the stabilizing impurity content, there are two phases of zirconium dioxide tetragonal modification with different tetragonality factors, c/a = 1.006–1.007 and 1.014–1.015, the first being nontransformable and the second being transformable to a monoclinic phase. All the synthesized crystals are characterized by a pronounced twin domain structure, which forms upon cooling the single crystal during the transition of the cubic structure to the tetragonal one. It was established that the Y₂O₃ concentration in the range from 2.5 to 3.0 mol % is optimal for ensuring high values of the strength characteristics and fracture toughness of the material. Doping of the crystals with the rare-earth elements notice-ably affects their strength characteristics. One of the most promising materials for fabricating cutting blades of the electrosurgical tool is the crystals of partially stabilized zirconium dioxide doped with Ce₂O₃+Nd₂O₃, which are characterized by high fracture toughness and enhanced bending strength.     

Nanocrystallisation of an Fe44.5Co44.5Zr7B4 amorphous magnetic alloy

The crystallisation of amorphous Fe_44.5Co_44.5Zr₇B₄ was investigated using DSC, electrical resistivity, TEM, HRTEM, CBED and VSM. Melt-spun amorphous Fe_44.5Co_44.5Zr₇B₄ crystallised by the primary crystallisation mode: the DSC results showed two exothermal peaks during heating. The electrical resistivity dropped sharply during the crystallisation event, which was consistent with DSC characterisation. From TEM, HRTEM and CBED results, primary crystallisation products which appeared to be clusters of crystals were found to be single crystal precipitates; these crystals formed in a compact dendritic morphology. Direct measurement of nucleation density and volume fraction was carried out using TEM analysis. The nucleation density was found to be high even in the absence of copper addition. The crystal growth was slow when the average size reached around 30?nm; this resulted in a stable nanocrystalline structure. The soft magnetic properties were improved after nanocrystallisation, the magnetic properties were related to the crystalline volume fraction and the Herzer model.     

The synthesis and characterization of Ti/SnO2-Sb2O3/PbO2 electrodes: The influence of morphology caused by different electrochemical deposition time

For the electrochemical oxidative degradation of wastewater, it is crucial for electrodes to be highly catalytic active, stable in performance and inexpensive in price. This study focuses on the preparation of the Ti/SnO₂-Sb₂O₃/PbO₂ anodes by anodic deposition under galvanostatic conditions and their electrocatalytic activity affected by crystal structure and surface roughness under different electrochemical deposition time, with phenol taken as the model pollutant to evaluate the electrocatalytic activity. The electrode surface morphology is characterized by XRD and SEM-EDX. The treatment effect of phenol is reflected by electrochemical analysis like CV and LSV. An important conclusion from experiment is that electrochemical deposition time has a major impact on electrocatalytic activity with the optimal deposition time observed around 30 min. At both deposition time beyond this optimal time window, electrocatalytic activity of phenol is substantially lowered. Increasing in electrochemical deposition time leads to a more uniform and smooth electrode surface, which enjoys a more compact structure than the “cracked-mud” one but lower specific surface area and catalytic activity. On the contrary, the “cracked-mud” structure means potentially a unique porous structure, which makes morphology at 30 min a perfect one for high electrocatalytic activity.     

The effect of In doping on optical properties of Fe:LiNBO3 crystals

Fe:LiNbO₃ and In:Fe:LiNbO₃ crystals were grown by Czochralski method. The absorption spectra were measured to investigate their defect structure. The photo damage resistance and photorefractive properties were measured. The photo damage resistance of the In:Fe:LiNbO₃ crystal in which the In concentration is above the threshold value is one order of magnitude higher than that of the Fe:LiNbO₃ crystal. The mechanisms of the violet shift of the absorption edge and the enhancement of the photorefractive effect of In:Fe:LiNbO₃ crystals were investigated.     

Nanodendritic Platinum Supported on γ‐Alumina for Complete Benzene Oxidation

The morphology of the platinum (Pt) nanoparticles has a significant effect on their activity for the catalytic oxidation of the volatile organic compounds (VOCs). In this work, the preparation of the dendritic and spherical Pt by a solution‐based approach is reported, which is supported on γ ‐ Al₂O₃ substrates, for decreasing the temperature of the complete conversion of benzene, one of the representative contaminants among the VOCs because of its carcinogenicity. The X‐ray photoelectron spectroscopy analyses reveal that the surface adsorbed oxygen is crucial for catalytic performance, and the electron transference from Pt to O is a benefit for the activation of oxygen. H₂‐TPR results indicate that the reducibility of the catalyst has a significant effect on the catalytic activity for the catalytic oxidation. In general, the dendritic Pt/Al₂O₃ catalysts, which possess more abundant and active surface adsorbed oxygen, exhibit the higher activity for the complete catalytic conversion of benzene compared with the spherical one. Moreover, the addition of a small amount of Ag (or Au), which is in order to ensure the dendritic structure, has little influence on the catalytic activity. The versatile solution‐based synthesis will be a promising method for creating the highly efficient catalysts for environmental remediation.     

Preparation and characterization of hybrid nanoparticles based on chitosan and poly(methacryloylglycylglycine)

CeO₂–MnO _x composites possessing rod-like morphology (fixed mole proportion of Ce/Mn) were synthesized through hydrothermal method and chosen as supporters to load PdO nanoparticles (PdO/Ce _x Mn_1–x ). The size of loaded PdO nanoparticles is about 2 nm. The catalytic behaviors of supported catalysts were examined through the complete catalytic oxidation of benzene. The results illustrated that the activities of supported catalysts were enhanced greatly as compared to unsupported, and the completely conversion temperature of benzene was reduced to ca. 250 °C. The effect of noble metal species (PdO) addition on the catalytic property and crystal structure of composites was researched in detail. The data revealed that the interaction between PdO and supporter, and intrinsic properties of supporter resulted in the enhancement of catalytic abilities.     

Understanding CeO2‐Based Nanostructures through Advanced Electron Microscopy in 2D and 3D

Engineering morphology and size of CeO₂‐based nanostructures on a (sub)nanometer scale will greatly influence their performance; this is because of their high oxygen storage capacity and unique redox properties, which allow faster switching of the oxidation state between Ce⁴⁺ and Ce³⁺. Although tremendous research has been carried out on the shape‐controlled synthesis of CeO₂, the characterization of these nanostructures at the atomic scale remains a major challenge and the origin of debate. The rapid developments of aberration‐corrected transmission electron microscopy (AC‐TEM) have pushed the resolution below 1 Å, both in TEM and in scanning transmission electron microscopy (STEM) mode. At present, not only morphology and structure, but also composition and electronic structure can be analyzed at an atomic scale, even in 3D. This review summarizes recent significant achievements using TEM/STEM and associated spectroscopic techniques to study CeO₂‐based nanostructures and related catalytic phenomena. Recent results have shed light on the understanding of the different mechanisms. The potential and limitations, including future needs of various techniques, are discussed with recommendations to facilitate further developments of new and highly efficient CeO₂‐based nanostructures.     

Structure and magnetic properties of cobalt-intercalated layered InSe crystals

We study the structure and magnetic properties of Co _x InSe layered crystals electrochemically intercalated by cobalt in a constant magnetic field. It is found that impurity clusters consisting of cobalt nano-particles with the fcc structure are formed in the intercalates under investigation on the Van der Waals planes in the space between the layers. Intercalates Co_0.1InSe obtained by implantation in a magnetic field exhibit a change in their magnetic properties (dependence of the magnetic moment in the magnetic field strength has the form of a hysteresis loop, which is typical of ferromagnetic materials).     

Photoelectric properties of Al/In<Subscript>2</Subscript>Se<Subscript>3</Subscript> Schottky barriers

We used directional solidification of the melt to grow single crystals of the binary compound In2Se3 and then determined the composition of the crystals obtained and their structure. From Hall effect measurements, we determined the type of conductivity, the concentration, and the Hall mobility of the free electrons in the single crystals obtained, on which we developed photosensitive Al/In₂Se₃ Schottky barriers for the first time and determined their photoelectric properties. We established that the indicated barriers can be used to design broadband optical photoconverters based on In₂Se₃ single crystals. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 425–427, May–June, 2008.     

Synthesis and optical properties of red emitting Eu doped CaZrO3 phosphor

Eu³⁺ activated Ca_1−xEu_xZrO₃ (x = 0.01–0.05) phosphor with perovskite structure has been synthesized by sol–gel combustion method. The structure, morphology and optical properties of materials were characterized by X-ray diffraction, scanning electron microscopy and fluorescence spectrometry. The XRD results indicate that crystals of CaZrO₃:Eu³⁺ belongs to orthorhombic perovskite structure. The phosphors can be effectively excited by UV light and the emission spectra results indicate that red luminescence of CaZrO₃:Eu³⁺ due to electric dipole transition ⁵D₀ → ⁷F₂ at 616 nm is dominant. Thus, these prepared phosphors show remarkable luminescent properties which find applications in display devices.     

Plasma density measurement in a gas-filled X-band backward wave oscillator with a double conversion heterodyne microwave interferometer

Plasma density was measured with a heterodyne microwave interferometer in both a gas-filled X-band backward wave oscillator (BWO) and in a smooth tube. Plasma is generated by impact ionization of a 650 kV, 2 kA electron beam. For fixed gas pressure we found that the plasma density rise in the operating BWO was much faster than in a smooth tube, indicating that Trivelpiece-Gould modes, or high power microwaves, increase plasma generation. Additional plasma enhanced BWO microwave output power. Measured plasma density at optimum power levels was n_cr ≈ 6 × 10¹²cm⁻³ at onset of emitted microwaves.     

Photoelectric Properties of p-GaSe/n-CdGa2S4 Heterostructures

Single crystals of the ternary compound CdGa₂S₄ have been grown from the melt by the Bridgman–Stockbarger method and their composition, structure, and electrophysical properties have been determined. From the crystals obtained, p-GaSe/n-CdGa₂S₄ heterostructures have been generated for the first time and their photoelectric properties in natural and linearly polarized light have been investigated. We determine the main parameters of the heterostructures and show that they can be used in photoprocessors of optical radiation.     

Enhanced photoelectrochemical properties of F-containing TiO2 sphere thin film induced by its novel hierarchical structure

The novel nanostructured F-containing TiO₂ (F-TiO₂) sphere was directly synthesized on the surface of Ti foil in the solution of NH₄F and HCl by one-step hydrothermal approach under low-temperature condition. The samples were characterized respectively by means of field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that the F-TiO₂ sphere was hierarchical structure, which composed of porous octahedron crystals with one truncated cone, leading to a football-like morphology. XPS results indicated that F⁻ anions were just physically adsorbed on the surface of TiO₂ microspheres. The studies on the optical properties of the F-TiO₂ were carried out by UV-vis light absorption spectrum. The surface fluorination of the spheres, the unique nanostructure induced accessible macropores or mesopores, and the increased light-harvesting abilities were crucial for the high photoelectrochemical activity of the synthesized F-TiO₂ sphere for water-splitting. The photocurrent density of the F-TiO₂ sphere thin film was more than two times than that of the P25 thin film. Meanwhile, a formation mechanism was briefly proposed. This approach could provide a facile method to synthesize F-TiO₂ microsphere with a special morphology and hierarchical structure in large scale.