Titanium nanocarbides: Synthesis and modeling

The present state of research on the production and modeling of nanostructures based on titanium carbide-a typical representative of an extensive class of carbides of d-and f-metals-is reviewed. Methods for the synthesis of various Ti-C nanostructures (molecular clusters, nanocrystallites, nanospheres, nanofibers, nanowires) are examined, and their morphology, atomic structure, and known physicochemical characteristics are described. Theoretical models of the atomic structure and properties of new types of nanostructures in the titanium-carbon system (endo-and exohedral titanofullerenes, “hybrid” structures based on carbon nanotubes, the so-called peapods, nanocables, and a number of others) and the prospects for their application as components of nanoceramics, hydrogen accumulators, materials for spintronics, etc. are discussed. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 1–23, January–February, 2007.     

Modeling of the structure and electronic structure of condensed phases of small fullerenes C<Subscript>28</Subscript> and Zn@C<Subscript>28</Subscript>

A comparative analysis of the stability factors and electronic structure of two possible crystalline forms of small fullerene C₂₈ and endohedral fullerene Zn@C₂₈ with diamond and lonsdaleite structures is performed using a cluster model. Atoms of elements that, when placed inside C₂₈ cages, have no significant effect on the stability of free small-fullerene molecules are shown to be able to dramatically change the electronic properties and reactivity of the C₂₈ skeleton and to be favorable for forming small-fullerene crystalline modifications, which are covalent crystals. In contrast, if the presence of foreign atoms inside C₂₈ cages stabilizes the isolated nanoparticles, then molecular crystals (such as C₆₀ fullerites) are formed due to weak van der Waals forces.     

A study of the valence state of the titanium atoms in nonstoichiometric carbides from the X-ray emission spectra and the results of an MO LCAO calculation

Journal of Structural Chemistry -     

Atomic structure and electronic properties of nanopeapods: Isomers of endohedral dititanofullerenes Ti2@C80 in carbon nanotubes

The atomic structure, charge and electronic parameters, and energies of formation of new “hybrid” nanostructures-nanopeapods Ti₂@C₈₀@C-NTs, regular linear ensembles of seven isomers of endohedral dititanofullerenes Ti₂@C₈₀ encapsulated into a carbon zigzag (19.0) nanotube—have been calculated by the self-consistent density functional tight-binding method (DFTB). The results are discussed in comparison to the “free” isomers of C₈₀ fullerenes and Ti₂@C₈₀ endofullerenes, as well as to all-carbon nanopeapods, i.e., C₈₀ isomers inside a carbon nanotube (C₈₀@C-NT). It is demonstrated that the type of Ti₂@C₈₀ isomer determines the energy effect of its encapsulation into the tube (exo-or endothermic), the orientational arrangement of end-ofullerenes in the tube, the charge states of the Ti₂@C₈₀ and tube atoms, and the electronic properties of nanopeapods (semiconducting or metallic).     

Electronic structure of niobium-doped molybdenum disulfide nanotubes

The effect of doping transition metal disulfide nanotubes on their structural and electronic properties was studied for the first time using self-consistent band-structure calculations by the density functional tight-binding method (DFTB). The influence of partial Nb → Mo substitution in the walls of MoS₂ nanotubes of various diameters and atomic configurations (armchair and zigzag) on their electronic structure, structural parameters, and relative stability is exemplified by a series of “mixed” Mo_0.9Nb_0.1S₂ nanotubes. The electronic properties of Mo_0.9Nb_0.1S₂ nanotubes are discussed as a function of the possible types of distribution of doping Nb atoms in the tubes.     

The numerical modeling of the composition and state of aggregation of the condensed medium formed in heating the Bi2O3 oxide in argon

The paper presents the results of the thermodynamic modeling of the composition and state of aggregation of the condensed medium formed in a Bi₂O₃-Ar medium at 9.8066 × 10^?2 MPa over the temperature range 300–1300 K. The possible presence of the Bi₂O₃, BiO, Bi₂O₅, and BiO₂ oxides in the solid and liquid states was taken into account. Temperature-induced changes in the solid and liquid solution components (bismuth oxides in various states of aggregation) are discussed.     

Electronic structure and chemical bonding in nonstoichiometric zirconium nitrides

X-ray emission spectra were taken and band calculations using the Green function LMTO method and cluster calculations using the discrete variational X method were carried out for the electronic structure and chemical bonding parameters for nonstoichiometric zirconium nitrides containing metallic and metalloid vacancies. The existence of structural defects leads to a redistribution of the occupancies of the major sub-bands of the nitride valence spectrum and the formation of a new group of states between the p-d- and d-like bands of ZrN_1.0.Institute of Chemistry, Urals Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 82–89, September–October, 1989.     

Electronic structure and chemical bonding in K<Subscript>2</Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript>

The calculations of the electronic structure of layered polyvanadate K₂V₃O₈ were made employing the spin-polarized tight-binding LMTO method. Calculated magnetic moment for K₄V₆O₁₆ compound phase equals 1.97 μ_B. V-O interactions were established to be dominating in the chemical bonding generation in this polyvanadate according to the estimated crystal orbital overlap population. The covalent bonds V(2)-V(2) in V(2)₂O₇ groups and electron density localization on vanadium atoms in isolated pyramids V(1)O₅ were found.     

Electronic structure of Nb x Ta1−x C alloys

Institute of the Chemistry of Solids, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 1, pp. 130–134, January–February, 1994.