Synthesis,structure, and properties of BIFENBVOX

Solid solutions Bi₄V_2-x Fe _x/2Nb _x/2O_11-δ (х?=?0.05–1.0) and Bi₄V_2-х-y Fe _x Nb _y O_11–δ (with fixed x or y?=?0.2 and variable х or y?=?0.2–0.5 with step 0.1) were synthesized by the standard ceramic technology in the temperature range 773–1113 K and by mechanochemical activation method using Bi₂O₃, V₂O₅ Fe₂O₃, and Nb₂O₅ oxides as initial compounds. The formation of solid solutions was studied. Ranges of stability and temperature values of phase transitions for different polymorphous modifications were defined using dylatometric and thermo gravimetric studies. The morphology and the local chemical composition of the ceramic samples were studied. Samples with concentration of dopants x?>?0.3 contain two phases; both major and impurity phases are solid solutions of the BIFENBVOX type although the dopants atoms distribution between them is random. The thermal expansion coefficients (TEC) were measured. The electrical conductivity of ceramic samples was investigated in a wide range of temperatures. The highest conductivity values among the studied solid solutions are observed for the sample with a small amount of dopants x?=?0.25.     

Synthesis,properties, and applications of fractionated nanodiamonds

The methods for dispersing nanodiamond powders of different purity grades and preparing nanodiamond powder suspensions suitable for fractionation are analyzed. The main physicochemical properties of fractions separated from the synthesis products (blends) and purified nanodiamonds are investigated. It is found that the size distribution of nanodiamonds in the blend is inhomogeneous: an increase in the particle size leads to a decrease in the fraction of these particles. The advantages of nanodiamonds fractionated in size are demonstrated for different applications.     

Structure, electron-accepting properties, and reactivity of nitrostilbenes

Nitrostilbenes, nitrostyrenes, nitrotoluenes, and nitrodibenzyls in neutral, radical anion, and dianion forms are studied by quantum chemical, electron spectroscopy, ESR spectroscopy, and cyclic voltammetry methods. The calculated electron affinities of nitroarenes are compared with electrochemical reduction potentials. The dianion form of stilbene is stable provided that it has two nitro groups in the para-position of the benzene ring. Nitrodibenzyls are converted to the corresponding nitrostilbenes by electrochemical reduction;this is explained by dissociative cleavage of C−H bonds in the trianion radical form of dibenzyl. In reactions of nitroarenes with bases, regioselectivity is determined by spin density distribution and by the conformation composition of the radical anions. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 4, pp. 640–654, July–August, 1998.     

Optical properties of calaverite,AuTe2

The optical properties of incommensurately modulated calaverite (AuTe₂) are presented. The surfaces of two melt-grown crystals were mechanically polished and turned out to be optically isotropic for reflection measurements. The surfaces recrystallized in several days. On recrystallizing optical anisotropy increased and a plasmon peak developed.     

Structural properties, conformational stability and oxygen binding properties of Penaeus monodon hemocyanin

Hemocyanin sequences allineament shows the presence of highly invariant regions especially in the active site and in the tight intersubunits interaction sites. Comparing the aminoacids in contact regions between monomers is possible to interpret the stability of hexamers.     

Laser properties of yag: Nd,Cr, Ce

Summary Transient absorption of a long lifetime ( 20 s) of YAG: Nd is typical of pure material. It is the main reason of thermal deformation of the laser rods accompanied with power decreases at higher CW input. It may be prevented by an admixture of Fe, Ti or Cr. Using a small admixture ( 10^–3 wt.%) of Ti or Cr the energy transfer among Nd ions and the gain coefficient may be increased. Cr in a higher concentration absorbs the pumping light and serves as earlier described coactivator (sensitizer) only. Fe impurity fully prevents any increase of the gain of YAG: Nd containing Ti or Cr and causes slow but irreversible degradation of the active parameters. Ce favourably modifies properties of YAG: Nd, Cr. YAG: Nd, Cr, Ce free of iron impurity is advisable active material for powerfull CW lasers.     

Dielectric properties of natural,modified, and irradiated zeolites

The complex permittivity (ɛ = ɛ′ − iɛ″) of natural, modified, and irradiated zeolites as a function of the frequency of a variable electric field is measured. For Ba²⁺-modified (doped) zeolite, the permittivity and dielectric loss tangent (tanδ) as functions of the electric field frequency are found to decrease monotonically. When the irradiation dose rises to 10⁵ cm⁻², the dielectric loss tangent reaches a maximum and then, starting from a dose of 3 × 10¹⁶ cm⁻², sharply drops. Such behavior of tanδ is assumed to be associated with Ba²⁺- and irradiation-induced structural modifications in the unit cell of zeolite.     

Fabrication,properties, and applications of flexible magnetic films

Flexible magnetic devices, i.e., magnetic devices fabricated on flexible substrates, are very attractive in applications such as detection of magnetic field in an arbitrary surface, non-contact actuators, and microwave devices, due to their stretchable, biocompatible, light-weight, portable, and low cost properties. Flexible magnetic films are essential for the realization of various functionalities of flexible magnetic devices. To give a comprehensive understanding for flexible magnetic films and related devices, recent advances in the study of flexible magnetic films are reviewed, including fabrication methods, magnetic and transport properties of flexible magnetic films, and their applications in magnetic sensors, actuators, and microwave devices. Our aim is to foster a comprehensive understanding of these films and devices. Three typical methods have been introduced to prepare the flexible magnetic films, by deposition of magnetic films on flexible substrates, by a transfer and bonding approach or by including and then removing sacrificial layers. Stretching or bending the magnetic films is a good way to apply mechanical strain to them, so that magnetic anisotropy, exchange bias, coercivity, and magnetoresistance can be effectively manipulated. Finally, a series of examples is shown to demonstrate the great potential of flexible magnetic films for future applications.     

Morphology,conductivity, and mechanical properties of polypyrrole-containing composites

An electrical-conducting polypropylene/polypyrrole (PP/PPy) composite was prepared by the chemically oxidative modification reaction of pyrrole on the surface of PP particles in suspension. Another type of PP/PPy composite was prepared by mixing the coated PP particles with noncoated PP particles at room temperature. The composites were processed by compression molding or by injection molding. The injection-molded composites exhibited better mechanical properties compared to compression-molded samples, while these composites showed better antistatic behavior and electrical conductivity. The differences in the behavior of the two types of composites were caused by the different structure of the PPy phase, which was studied by hot-stage optical microscopy and X-ray photoelectron spectroscopy (XPS).     

Structural,electronic, and optical properties of beryllium monochalcogenides

The results of first-principles theoretical study of the structural, electronic and optical properties of beryllium monochalcogenides BeTe, BeSe and BeS, performed using the full potential linearized augmented plane wave (FP-LAPW) method are presented. The calculated structural parameters and band gaps compare very well with previous theoretical results. The trends of the band gap pressure coefficients and volume deformation potentials for these II-VI compounds are investigated. The linear pressure coefficients for the X and band gaps increase with decrease in anion atomic weight. The dependence of the direct and indirect band gaps on the relative change of lattice constant are found to follow almost the same type of trends in each of these compounds. The volume deformation potential ( ) for the direct ( ) and indirect ( ) gaps are positive, but negative for the indirect ( ) gap. Furthermore, , for transitions decreases with increase in anion atomic number whereas , increases. The optical properties have also been calculated. From the reflectivity spectra, the compounds will be useful for optical applications. The variation of the band gaps with respect to the application of pressure and the origin of some of the peaks in the optical spectra are discussed in terms the calculated electronic structure.Received: 26 September 2003, Published online: 18 June 2004PACS: 71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.) - 71.15.Mb Density functional theory, local density approximation, gradient and other corrections - 71.20.Nr Semiconductor compounds     

Transient electromagnetic properties of two,infinite, parallel wires

An analysis is presented of the transient electromagnetic field around two parallel wires. It is shown that the field can be expressed in terms of a discrete spectrum and a continuous spectrum. The discrete part of the spectrum can be interpreted as modes whose properties are investigated. The time history of the current at different points on the wires is also calculated when each wire is excited by a slice generator with a step-voltage source. Two different modes of excitation are considered: 1) the two voltage generators have equal strength but opposite polarity, and 2) they have equal strength and same polarity. With the first type of excitation the induced current on the wires can be described accurately by the TEM mode alone provided that one transit time or so between the wires has elapsed after the passage of the wavefront.     

Structural, electronic, and magnetic properties of Co-doped ZnO

Density functional theory based calculations have been carried out to study structural, electronic, and magnetic properties of Zn1-xCoxO (x = 0, 0.25, 0.50, 0.75) in the zinc-blende phase, and the generalized gradient approximation proposed by Wu and Cohen has been used. Our calculated lattice constants decrease while the bulk moduli increase with the increase of Co 2+ concentration. The calculated spin polarized band structures show the metallic behavior of Co-doped ZnO for both the up and the down spin cases with various doping concentrations. Moreover, the electron population is found to shift from the Zn-O bond to the Co-O bond with the increase of Co 2+ concentration. The total magnetic moment, the interstitial magnetic moment, the valence and the conduction band edge spin splitting energies, and the exchange constants decrease, while the local magnetic moments of Zn, Co, O, the exchange spin splitting energies, and crystal field splitting energies increase with the increase of dopant concentration.     

Tribological properties of dry,fluid, and boundary friction

A friction pair is studied under lubricant-free dry friction, hydrodynamic, and boundary lubricant conditions. It is shown that, in dry friction, the number of harmonics in the time dependence of the coordinate of the lower rubbing block decreases with increasing frequency of an applied periodic action until the interacting surfaces stick when a critical frequency is exceeded. The surfaces then move together. The behavior of a friction pair with a lubricant made of a Newtonian fluid, pseudoplastic fluid, or dilatant non-Newtonian fluid is analyzed in the hydrodynamic case. It is found that a pseudoplastic fluid or a boundary lubricant leads a intermittent (stick-slip) friction mode, which is one of the main causes of fracture of rubbing parts, over a wide parametric range.     

Electric,magnetic, and thermal properties of quasicrystal-forming melts

The electric resistance, magnetic susceptibility, and specific heat of the icosahedral phases of the Al-Cu-Fe system have been examined in the melt region. It has been shown that the features of the properties of a homogeneous solid state, as well as correlations between these features, hold in melts up to temperatures above the melting point by several hundreds of degrees. The results indicate that the short-range order and orbital hybridization determine the mechanism responsible for the electronic spectrum and ultrahigh-resistance state of quasicrystals.     

Structural, electronic, and chemical properties of nanoporous carbon

Nanoporous carbon (NPC) exhibits unexplained chemical properties, making it distinct from other graphenelike materials, such as graphite, fullerenes, or nanotubes. In this Letter, we analyze the properties of NPC in terms of its structural motifs, which are derived from defects in distorted graphene sheets. Our density-functional theory calculations show that these motifs can be present in high concentration (up to 1%). Some of them induce localized levels close to the Fermi level, therefore leading to local charging and controlling the material's chemical function, for example, as a catalyst.