Computational Study of Structure and Thermochemistry of Some Endo‐ and Exohedral Fullerene Derivatives

Abstract

DFT calculations were applied to the problem of fullerene isomerism. Two classes of thermally stable fullerene derivatives are considered: endohedral metallofullerenes, which in some cases reveal carbon cage topology different from that observed in the empty fullerenes of the same size, and fullerene fluorides, which have uniquely rich number of theoretically possible isomers.     

Structural and Electrical Properties of Fluorine Doped (Bi, Pb)-1212 Ceramics

In the aim to test the effect of fluorine doping on structural and electrical properties of semiconducting Bi(Pb)-1212 phase, bulk samples with nominal composition of Bi_0.4Pb_0.35Sr₂Y_0.8Ca_0.2Cu_2.05O _y F _x with x=0,0.2,0.4 and 0.6 are prepared in air by solid state reaction method and characterized. Similarly to other Bi-based cuprates, the scanning electron microscopy shows that fluorine doping increases the grain size of the samples. The obtained X-ray diffraction patterns are indexed in P4/mmm space group. A slight increase of cell volume by doping is revealed, a result which is in line with that seen in Y-123 compounds. Even if the resistivity decreases with fluorine content, all compounds exhibit a semiconducting behavior. The conduction mechanism obeys well to the two dimensional variable range hopping (2D-VRH) model from room temperature down to approximately 40 K. The analysis of the fitting results suggests that the improvement of electrical conduction could be due to a delocalization of charge carriers.     

Structural and Electrical Properties of Cobalt Ferrite

Ferrites are a class of cohesive new materiafs required for many specialised applications. Cobalt ferrite (CoFe2O4) has been identified as a substitute for carbon and serves as a non consumable anode for an eco-friendly and energy efficient production of aluminium. Pellets of cobalt ferrite have been prepared by powder metallurgical process and their electrical properties have been investigated from ambient temperature to 1273 K. The structural and morphological features have been studied by X-ray diffraction and scanning electron microscopy The relationships between such properties, chemical composition and sintering temperatures are thoroughly discussed.     

Theory of the Relaxation Spectra of Cross‐Linked Polymers in the Presence of Structural and Dynamic Heterogeneity

The spectra of relaxation times of polymer meshes in the presence of various types of structural and dynamic heterogeneity have been considered. The influence of the orientation ordering of elements of macromolecules between the mesh nodes on the intrachain spectrum has been investigated. Analysis of the interchain largescale processes in polymer meshes containing rodlike inclusions has been carried out. It has been shown that the presence of structural and dynamic heterogeneity of the above types along with the previously considered domain structure of crosslinked polymers leads to a fine structure of the relaxation spectra of polymer meshes.     

Synthesis and Electronic Properties of Transition Metal Containing Polymers

1. Introduction Since the discovery of the first organic light emitting polymer in 1991, research in this area has been mainly focused on conjugated organic polymers. The use of polymer metal complexes for electroluminescence applications has received relatively few attention.     

Electron–Phonon Coupling and Properties of Doped BaBiO3

Density functional calculations based on local density approximation (LDA) of the properties of doped barium bismuthates are reported. Using a linear-response approach within the linear-muffin-tin-orbital method the phonon spectrum of Ba_0.6K_0.4BiO₃ is calculated. The electron–phonon coupling constant is then evaluated for a grid of phonon wavevectors using the self-consistent change in the potential due to phonon distortion. Anharmonic contributions to from the tilting of oxygen octahedra are also evaluated on the basis of the frozen-phonon approach.     

Influence of Structural Effects on the Superconductivity of Ammonia‐Doped NaK2C60

Abstract

The role of structural effects on the anomalous superconducting properties of (NH₃) _x NaK₂C₆₀ fullerides was investigated using ²³Na and ²H NMR. In the metallic (NH₃) _x NaK₂C₆₀ (0.5 < x < 1) compounds, the ²³Na quadrupolar splitting is observed to be independent from ammonia concentration x which, on the other hand, substantially affects the superconducting transition temperature. The marginal influence of sodium cation displacement in the superconducting properties is confirmed also by the absence of any electric field gradients in the recently synthesized nonmagnetic insulator (NH₃)₂NaK₂C₆₀. ²H NMR measurements on deuterated samples enabled us to study the ND₃ reorientational dynamics, indicating a hampered ammonia rotation in the insulating (x = 2) case, where the Na⁺ ions become centered.     

Structural, Optical and Electrical Properties of Evaporated CdSe Films

CdSe films are of great interest for use in thin film photoelectric devices. A simple chemical precipitation method is adopted for the first time to synthesise CdSe powder. Films on glass obtained at different substrate temperatures TS such as 300, 373, 423 and 473 K have been characterised by X-ray diffraction, optical absorption and Hall measurements.     

First Principles Study of Structural, Magnetic and Electronic Properties of PbX (X= S and Se) Doped with B, C and N

Six ternary compounds PbA _0.75 M _0.25 (A=S and Se; M=B, C and N) with a NaCl structure were calculated to study the structure, electronic, and magnetic properties of them. The calculations were performed using the first-principles plane wave pseudopotential method within the generalized gradient approximation. The calculations reveal that ferromagnetism can be realized for C- and N-doping while B substitution does not induce magnetism in PbS and PbSe systems. The total energy calculations show that the ferromagnetic state is more stable as compared to a nonmagnetic state at their equilibrium lattices. Spin-dependent electronic band structure, total, and partial densities of state calculations demonstrate that the 2p-states of C- and N-dopants around Fermi level are responsible for ferromagnetism. Furthermore, equilibrium lattice constant, bond length, local magnetic moments, total magnetic moments, and robustness of ferromagnetism have been calculated. Particularly, the negative pressure calculations indicate that C-doping lead chalcogenides can change to half-metallic ferromagnetism materials.     

Synthesis and Complex Study of Water‐Soluble Polymer Derivatives of C60 Fullerene

Abstract

The water‐soluble composites with fullerene content up to 5 wt% based on poly‐(N‐vinylpyrrolydone) (PVP) were obtained. The higher fullerene content is achieved by means of introducing tetraphenylporphyrine (TPP) and KBr into composites. The synthesis includes the formation of C₆₀–TPP complex and its further interaction with polymer. The formation of C₆₀–TPP complex was confirmed by ¹³C NMR, SANS, and translational diffusion. The hydrodynamic and electrooptical studies of C₆₀–TPP–PVP complexes indicate the higher symmetry of the polymer coil in the complex as compared to PVP. The C₆₀–PVP–KBr composites were also obtained by the solid state interaction under vacuum, KBr promoting the destruction of fullerene aggregates.     

Transport Properties of Fullerene–Polyphenylene Oxide Homogeneous Membranes

Abstract

Fullerene–polyphenylene oxide (C₆₀–PPO) compositions containing up to 2 wt% C₆₀ were obtained and used for homogeneous membranes formation. Gas separation properties were estimated by measuring the permeability of individual gases H₂, O₂, N₂, CH₄, and CO₂. A correlation between gas permeability and free volume was established. The pervaporation of water/ethanol mixtures through fullerene‐containing membranes showed that C₆₀–PPO membranes exhibit dehydration properties. The degree of equilibrium sorption for PPO and C₆₀–PPO membranes in a water/ethanol system was estimated in the liquid phase. Gas separation and pervaporation properties were treated as a reflection of molecular interactions between PPO and C₆₀ molecules in compositions.     

HPLC Diode‐Array Analysis of C60 and C70 Polymeric Fullerene Oxides (Fullerene Polymeric Ozonides)

Abstract

It is shown by HPLC diode‐array analysis that the C₆₀ and C₇₀ polymeric fullerene oxides ([C₆₀]‐PFOs and [C₇₀]‐PFOs) which are polymeric ozonides, are composed by nine different components. The ozonide derivatives of C₆₀ and C₇₀ have been proved to be practically analogous in chemical structure and composition. The most important component of both [C₆₀]‐PFOs and [C₇₀]‐PFOs accounts for about 3/4 of each sample. The overozonation of [C₆₀]‐PFOs in methanol has been studied and shown to not produce any significant changes.     

Structural Phase Transitions of High-Pressure Li x Na1 – x NbO3 Solid Solutions

Li _x Na_{1 – x} NbO₃ (x = 0.125, 0.17, 0.25) solid solutions are synthesized at high pressures (6 GPa) and temperatures (1100–1500°C), and their polymorphic transformations are studied by x-ray diffraction. The composition and temperature dependences of lattice parameters for the identified polymorphs are presented. The results demonstrate that the high-pressure solid solutions with x = 0.17 and 0.25 are supersaturated under ordinary conditions. Heating these solid solutions to above 800°C leads to precipitation of an LiNbO₃-based phase.     

Structural and Electrical Transport Properties of Al1−xM x B2 (M = Li, Vacancy)

AlB₂ and MgB₂ are neighboring compounds and have similar crystal structures. However, their superconducting properties are very different because the σ holes which play a key role in the superconductivity of MgB₂ do not exist in AlB₂. In this paper we reported our attempts to dope holes into AlB₂ by substituting Li and vacancy for Al, and these holes were expected to induce superconductivity in the system. However, experimental results showed that Li was hard to substitute Al in AlB₂. The variation of resistivity with temperature and x for samples with the nominal composition of Al_1?xLi _x B₂ was analyzed by considering the phase variation of the samples with x. The temperature dependence of resistivity for Al_1?xB₂ was also studied and orders of magnitude change in resistivity was observed when x was up to 0.4 and 0.5, similar to that observed in Mg_1?xB₂ system by Sharma et al. (A. Sharma, N. Hur, Y. Horibe, C. H. Chen, B. G. Kim, S. Guha, Marta Z. Cieplak, and S. W. Cheong, Phys. Rev. Lett. 89, 167003 (2002)). It is proposed that phase separation may exist in Al_1?xB₂, leading to the dramatic change of resistivity because of percolation.     

Effect of Titania Additive on Structural and Mechanical Properties of Alumina–Fluorapatite Composites

Mechanical properties of alumina-fluorapatite composites with different titania additive amounts (0, 0.5, 1, 1.4, 2, 3, 4 and 5 wt%) have been investigated between 1200 and 1600℃. The optimum values of densification and mechanical properties of composites have been reached with 1.4 wt% of titania after the sintering process at 1500℃ for 1 h. Thus, the rupture strength of alumina-26.52 wt% Fap-1.4 wt% TiO2 reaches 75 MPa. At higher temperature and beyond 1.4 wt% TiO2 ,the densification and mechanical properties were hindered by the formation of both intergranular porosity and secondary phase. X-ray diffraction (XRD) analysis of alumina-Fap-TiO2 composites shows the formation of aluminium titanate (Al2O3-TiO2:Al2TiO5 ). The 27Al magic angle scanning nuclear magnetic resonance analysis of Al2O3-Fap-TiO2 composites reveals the presence of octahedral and pentahedral aluminium and novel environment relative to tetrahedral aluminium sites.     

Structural, Electronic and Magnetic Properties of Nanolayer and?Bulk of MnCo2Si and MnFeCoSi Compounds

In the present work we have investigated the structural, electronic and magnetic properties of MnCo₂Si and MnFeCoSi in bulk and nanolayer using density functional theory. The total energies as a function of volume are calculated and thereby the bulk modulus and their pressure derivatives are determined. The effect of atoms at the surface of these nanolayers has been analyzed using the calculated total and partial electron density of states in its ferromagnetic phase. The spin-polarized density of states show that both bulk MnCo₂Si and MnFeCoSi present a half-metallicity, which is lost at their nanolayer surfaces. Furthermore, the effects of pressure on the magnetic moment of these compounds in its bulk form are investigated.     

On the Problem of Deposition of Wear‐ and Heat‐Resistant Coatings on Machine Parts

The content of doping elements as a function of the flow rate of the working gas (pressure), the wear resistance (the dopant is fluxcored wire), the thermal conductivity, the strength, the thermal stability, and the structure (the dopant is aluminum and Ni–Cralloy wires) have been investigated in coatings produced by the method of electricarc metallization.     

Vibrational measurements of Na/Ni(111) and (Na + CO)/Ni(111)

The vibrational properties of Na atoms and of Na coadsorbed with CO on Ni(111) have been studied by high-resolution electron energy loss spectroscopy. Loss measurements showed a significant weakening of the alkali–substrate bond as a function of the alkali coverage. Moreover, we found that coadsorbed CO molecules dramatically influence the vibrational properties of Na adatoms. The Na–Ni stretching frequency (22 meV) measured on the Na/Ni(111) system shifted down to 13 meV for the (Na + CO)/Ni(111) surface. This unexpected result was ascribed to a charge transfer from Na to CO. Present findings give new insights on the nature of the alkali–substrate and alkali–CO bond.     

Spectral Properties of a Doped Antiferromagnet with Pairing Correlations

In this paper, we study the spectral properties of a phenomenological model for a weakly doped antiferromagnet. In this model, it is assumed that each carrier moves in one of the two sublattices where it was introduced. Such a situation corresponds to a case of underdoped high-temperature superconductors with the free carrier spectra maximum at k=(±π/2,±π/2) and with a four-pocket Fermi surface. We study the spectral properties of the model by taking into account both the fluctuations of the phases of the superconducting order parameter and spins of the antiferromagnetic background. It is shown that the hole spectral function and the density of states are strongly affected by these fluctuations. In particular, we argue that these fluctuations can be responsible for the temperature evolution of the Fermi pockets in cuprate superconductors.     

Determination of the Chemical Potential of Mass‐ and Heat‐Transfer Processes in Porous Bodies

The problem of determining the chemical potential of mass and heattransfer processes for porous bodies of a classical shape (an infinite plate, a sphere, etc.) is considered; the solution obtained is illustrated with examples of the nonisothermal extraction and nonisothermal adsorption purification of vegetable oils.