Structure of smooth hydrocarbon CDx films with a high deuterium ratio x ~ 0.5 redeposited from T-10 tokamak D-plasma discharges (NRC Kurchatov Institute, Moscow) has been studied. For the first time, small and wide angle X-ray scattering technique using synchrotron radiation and neutron diffraction have been employed. A fractal structure of CDx films is found to consist of mass-fractals with rough border, surface fractals (with rough surface), plane scatterers and linear chains forming a branched and highly cross-linked 3D carbon network. The found fractals, including sp2 clusters, are of typical size ~1.60 nm. They include a C13 fragment consisting of three interconnected aromatic rings forming a minimal fractal sp2 aggregate 9 × C13. These graphene-like sp2 clusters are interconnected and form a 3D lattice which can be alternatively interpreted as a highly defective graphene layer with a large concentration of vacancies. The unsaturated chemical bonds are filled with D, H atoms, linear sp2 C=C, C=O, and sp3 structural elements like C-C, C-H(D), C-D2,3, C-O, O-H, COOH, CxD(H)y found earlier from the infrared spectra of CDx films, which are binding linear elements of a carbon network. The amorphous structure of CDx films has been confirmed by the results of earlier fractal structure modeling, as well as by researches with X-ray photoelectron spectroscopy which allow finding a definite similarity with the electron structure of their model analogues — polymeric a-C:H and a-C:D films with a disordered carbon network consisting of atoms in sp3 + sp2 states. 相似文献
The effect of nonstoichiometry and ordering on the lattice constant aB1 of the basic lattice of vanadium carbide VCy(0.65 < y < 0.875) is studied. A change in the lattice constant of disordered carbide VCy at the reduction of the carbon content is considered using the direction of static displacements of atoms near a vacancy. A model for the calculation of the basic lattice constant aB1 of vanadium carbide is proposed taking into account nonstoichiometry and ordering. It is shown that the ordering of vanadium carbide VCy with the formation of V6C5 and V8C7 superstructures results in an increase in the basic lattice constant as compared to disordered carbide. 相似文献
The elastic moduli and elastic constants of the ternary semiconductor alloy AlyGa1-yAs at finite temperature have been investigated using the statistical moment method. The Young, shear, bulk moduli and elastic constants C11, C12, C44 of the zinc-blende AlyGa1?yAs crystal are calculated as functions of Al composition and temperature. Numerical calculations have been performed and compared with those of the experimental and other theoretical results showing the reasonable agreements. Our study shows that elastic moduli and C11, C12 constants of zinc-blende AlyGa1?yAs alloy are decreasing functions of the temperature and Al composition; C44 constant is a decreasing function of the Al composition. 相似文献
The effect of nonstoichiometry on the lattice constant of cubic vanadium carbide VCy (0.65 < y < 0.875) is studied. It is found that the ordering of vanadium carbide VCy with the formation of superstructures V6C5 and V8C7 leads to an increase in the base lattice constant in comparison with disordered carbide. Taking into account the change in the lattice constant, the direction of the static displacements of atoms near the vacancy is discussed. 相似文献
The magnetic and elastic properties of the Bi1-xCaxMnO3 manganites are studied. The phase transformations revealed are ferromagnet-spin glass (x≥0.15) and spin glass-charge-ordered antiferromagnet (x≥0.25). The ferromagnetic state is characterized by ordering of the Mn3+dx2-y orbitals. It is suggested that thespin glass state originates from local static Jahn-Teller distortions. The antiferromagnetic charge-ordered and the spin-glass disordered phases coexist in samples with 0.25<x<0.32, which may be due to the charge order-disorder phase transformation being martensitic in character. The magnetic phase diagram is constructed. 相似文献
LSDA + U + SO calculations of the electronic structure of helicoidal Fe1 - xCoxSi ferromagnets within the virtual crystal approximation have been supplemented with the consideration of the Dzyaloshinski-Moriya interaction and ferromagnetic fluctuations of the spin density of collective d electrons with the Hubbard interactions at Fe and Co atoms randomly distributed over sites. The magnetic-state equation in the developed model describes helicoidal ferromagnetism and its disappearance accompanied by the occurrence of a maximum of uniform magnetic susceptibility at temperature TC and chiral fluctuations of the local magnetization at T > TC. The reasons why the magnetic contribution to the specific heat at the magnetic phase transition changes monotonically and the volume coefficient of thermal expansion (VCTE) at low temperatures is negative and has a wide minimum near TC have been investigated. It is shown that the VCTE changes sign when passing to the paramagnetic state (at temperature TS). 相似文献
The atomic and electronic structures of metal-rich noncentrosymmetric zirconium oxide synthesized by the ion beam sputtering of a metallic target in an oxygen atmosphere has been studied by X-ray photoelectron spectroscopy, Raman scattering, spectral ellipsometry, and quantum-chemical simulation. It has been established that ZrOx < 2 consists of ZrO2, metallic Zr, and zirconium suboxides ZrOy. The stoichiometry parameter of ZrOy has been estimated. It has been shown that the optical properties of ZrOx < 2 are determined by metallic Zr. A model of fluctuation of the width of the band gap and a potential for electrons and holes in ZrOx < 2 based on spatial fluctuations of the chemical composition has been proposed. 相似文献
The conditions for the existence of discrete breathers (DBs) in biatomic crystals of AB and A3B composition are established, and their properties are studied by means of molecular mechanics using the examples of CuAu and Pt3Al, respectively. The phonon spectra of the crystals are analyzed, and a gap in the phonon spectrum of CuAu is obtained via considerable homogeneous elastic strain. There is a gap in the phonon spectrum of the Pt3Al crystal at zero strain, due to the considerable difference between the atomic weights of its components. The frequencies at which discrete breathers can exist in the considered crystals are determined. The energy localized on different types of DBs is estimated. The propagation of a current pulse through Pt3Al resulting in the excitation of DBs with mild nonlinearity is simulated. 相似文献
The optical properties of GeOx film and GeOx/SiO2 multilayer heterostructures (with thickness of GeOx layers down to 1 nm) were studied with the use of Raman scattering and infrared spectroscopy, ellipsometry and photoluminescence spectroscopy including temperature dependence of photoluminescence. The observed photoluminescence is related to defect (dangling bonds) in GeOx and interface defects for the case of GeOx/SiO2 multilayer heterostructures. From analysis of temperature dependence of photoluminescence intensity, it was found that rate of nonradiative transitions in GeOx film has Berthelot type, but anomalous deviations from Berthelot type temperature dependence were observed in temperature dependences of photoluminescence intensities for GeOx/SiO2 multilayer heterostructures. 相似文献
Metal nanoparticles have been combined with magnet metal–organic frameworks (MOFs) to afford new materials that demonstrate an efficient catalytic degradation, high stability, and excellent reusability in areas of catalysis because of their exceptionally high surface areas and structural diversity. Magnetic MxOy@N-C (M = Fe, Co, Mn) nanocrystals were formed on nitrogen-doped carbon surface by using 8-hydroxyquinoline as a C/N precursor. The Co@N-C, MnO@N-C, and Fe/Fe2O3@N-C catalysts were characterized by X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), N2 adsorption/desorption, and X-ray photoelectron spectroscopy (XPS). The catalytic performances of catalysts were thoroughly investigated in the oxidation of aniline solution based on sulfate radicals (SO4?.) toward Fenton-like reaction. Magnetic MxOy@N-C exhibits an unexpectedly high catalytic activity in the degradation of aniline in water. A high magnetic MxOy@N-C catalytic activity was observed after the evaluation by aniline degradation in water. Aniline degradation was found to follow the first-order kinetics, and as a result, various metals significantly affected the structures and performances of the catalysts, and their catalytic activity followed the order of Co > Mn > Fe. The nanoparticles displayed good magnetic separation under the magnetic field.
Optical properties of amorphous nonstoichiometric tantalum-oxide films of variable composition (TaOx, x = 1.94–2.51) in the spectral range of 1.12–4.96 eV, obtained by ion-beam sputtering-deposition of metallic tantalum at different partial oxygen pressures (0.53–9.09 × 10–3 Pa), have been investigated. It is shown by spectral ellipsometry that the character of dispersion of the absorption coefficient and refractive index in TaOx of variable composition suggests that light-absorbing films with dispersion similar to that in metals are formed at oxygen pressures in the growth chamber below 2.21 × 10–3 Pa, whereas transparent films with dielectric dispersion are formed at pressures above 2.81 × 10–3 Pa. According to the data of quantumchemical simulation, the absorption peak at a photon energy of 4.6 eV in TaOx observed in the absorptioncoefficient dispersion spectrum is due to oxygen vacancy. The peak in the Raman-scattering spectra of TaOx films with metallic dispersion at frequencies of 200–230 cm–1 is presumably related to tantalum nanoclusters. 相似文献
Phonon spectra and phonon density of states of intermetallic compounds Ni3Al and NiAl are studied using the ab initio linear-response method. The calculated phonon dispersion curves agree well with the inelastic neutron scattering data available for the crystals under study. 相似文献
The capacitance-voltage and current-voltage characteristics of the n-CdS/p-CdTe heterosystem are investigated. Analysis of these characteristics demonstrates that the CdTe1?xSx solid solution formed at the n-CdS/p-CdTe heterointerface is inhomogeneous in both the conductivity and composition. The thickness of solid solutions is estimated from the capacitance-voltage characteristics. It is shown that, for the n-CdS/p-CdTe heterosystem, the current-voltage characteristic in the current density range 10?8-10?5 A cm?2 is governed by the thermal electron emission, whereas the current in the heterostructure at current densities in the range 10?4-10?2 A cm?2 is limited by recombination of charge carriers in the electroneutral region of the CdTe1?xSx solid solution. The lifetime and the diffusion length of minority charge carriers in the CdTe1?xSx solid solution and the surface recombination rate at the interface between the CdS layer and the CdTe1?xSx solid solution are determined. It is demonstrated that the n-CdS/p-CdTe heterostructure operates as a p-i-n structure in which CdTe is a p layer, CdTe1?xSx is an i layer, and CdS is an n layer. 相似文献
A comparative analysis of the results of the X-ray and Mösbauer studies of the high-temperature superconductor (HTSC) YBa2Cu3Oy and YBa2Cu3 ? x57FexOy (x = 0.015, Tc ≈ 91.5 K) samples with different average grain sizes <D> in the micron and submicron ranges has been performed. The regularities in the change in the lattice parameter c and in the degree of occupation of different oxygen sites in the CuOδ chain planes taking place at the decrease in <D> have been studied. The quantitative interrelation between the parameter c and the oxygen content δ in the CuOδ planes exceeding the amount of the mobile oxygen due to the interplane oxygen redistribution is established. 相似文献
The effect of white and UV radiation on the phase composition of amorphous CNx films are studied by X-ray diffraction analysis and visible-range spectroscopy. The films have variable-range atomic order and consist of amorphous graphite clusters (30 Å) crystalline clusters (50–100 Å) of graphite, diamond, and carbon nitride phases; and intercluster medium with long-range (1–2 Å) atomic order. It is shown that irradiation of the films by white light facilitates the growth of fine graphite clusters. Irradiation by UV light suppresses the growth of the graphite and carbon nitride phases, favoring the growth of the diamond phase (1.5%). It is demonstrated that a change in the mesoscopic phase composition of the CNx films causes a change in the energy gap width in the visible range from Eg = 0.75 eV for the films irradiated by white light to Eg = 1.75 eV for those exposed to UV radiation. 相似文献
Ferromagnetism and ferroelectricity in Eu monochalcogenides have been investigated by ab initio density functional theory in the DFT+U approach. Exchange interaction parameters and Curie temperatures under pressure are studied and discussed using Heisenberg Hamiltonian with first and second-nearest-neighbor interactions. The calculations showed that the hydrostatic pressure perfectly improves the Curie temperature (EuO: TC = 175 K; EuS: TC = 33.8 K) and in the other hand it cannot induce the spontaneous polarization (Ps). The effect of uniaxial and biaxial pressure is also studied. Although the uniaxial strains slightly increases the Curie temperature, it ensures the ferrolectricity in these systems by producing a spontaneous polarization of the order of Ps(EuO) = 57.50 μC/cm2 and Ps(EuS) = 42.86 μC/cm2 with pressures of 5% and 4%, respectively. The search for new model systems is a necessity to better understand the physics related to multiferroïc materials and to consider possible applications. 相似文献
Transmission electron microscopy has been used to study ball milled and H cycled NaAlH4 with 10 mol% TiCl3. Isolated from the main phases in this hydrogen storage system, nanocrystalline aggregates of fcc TiHx (0≤x<0.67) were found. The value of x was determined based on the assumption of a linear increase of the TiHx lattice parameter by increasing H content. The size of the TiHx crystallites was in the range 10 to 20 nm, and the lattice parameter decreased from 4.22 Å in TiH0.67 to 4.10 Å in pure fcc Ti. Non-equilibrium ball milling and subsequent H cycling in combination with a small crystallite size are believed to make the TiHx phase stable. The present results are the first observations of fcc TiHx with low hydrogen content, and the measured fcc lattice parameter of Ti matches first-principles calculations. 相似文献
Ginzburg-Landau (GL) theory is used to study surface superconductivity for UPt3 for various order parameter symmetries (OPS), andHc3 is found for all principal directions of the surface normal\(\hat n\) and the field [1]. Assuming specular reflection, and allowing for reorientation of the antiferromagnetic symmetry breaking field in the models withE1g,E2g,E1u, orE2u symmetry, the experiments of Keller et al. [2] with\(\hat n = \hat a\) can be qualitatively explained for all OPS except possiblyA1u⊕B1u. The implied GL parameters then predict qualitatively different and OPS dependent behavior for\(\hat n = \hat a^* \) and\(\hat n = \hat c\). Study ofHc3 for these surfaces would give strong clues about the OPS of UPt3. 相似文献
In this proceeding, we present our recent work on decay behaviors of the Pc hadronic molecules, which can help to disentangle the nature of the two Pc pentaquark-like structures. The results turn out that the relative ratio of the decays of Pc+(4380) to \({\bar D *}{\Lambda _c}\) and J/ψp is very different for Pc being a \({\bar D *}{\Sigma _c}\) or \(\bar D\Sigma _c *\) bound state with \({J^P} = \frac{{{3 - }}}{2}\) And from the total decay width, we find that Pc(4380) being a \(\bar D\Sigma _c *\) molecule state with \({J^P} = \frac{{{3 - }}}{2}\) and Pc(4450) being a \({\bar D *}{\Sigma _c}\) molecule state with \({J^P} = \frac{{{5 + }}}{2}\) is more favorable to the experimental data. 相似文献
Influence of temperature and magnetic field H on magnetism of spherical Gd nanoparticles of different sizes (89, 63, 47, 28, and 18 nm) was studied in the temperature range 250 K < T < 325 K. The particles were obtained by metal vapor condensation in the flow of helium. The particles with d = 18 nm did not show a magnetic transition; their structure is a combination of two cubic phases (FCC1 and FCC2). Large particles remained in the HCP phase and had an admixture of the FCC1 phase, the amount of which decreased as the particle sizes increased; magnetic transition took place at Tc = 293 K. The admixture of O2 did not alter the structure but decreased the magnetization σ and magnetic permeability μ. An orientation transition in polycrystalline gadolinium initiated by the magnetic field H was proved in an experiment. The orientation transition in Gd particles smaller than 63 nm, the magnetic structure of which is close to the single-domain structure, occurred near Tc without the influence of H. 相似文献