Microclusters as superatoms for developing new materials
TL;DR: In this paper, the authors present some recent developments in this direction and discuss bonding in such materials, and discuss how to construct new clusters and molecules which could be assembled to form new materials.
Abstract: With the discovery of solid C60, efforts are being made to develop new clusters and molecules which could be assembled to form new materials. Here we present some recent developments in this direction and discuss bonding in such materials.
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TL;DR: In this article, the atomic and electronic structure of divalent metals, aluminum and antimony, which exhibit a range of bonding characteristics e.g. non-metal-metal transition, metallic and covalent respectively, are analyzed.
Abstract: We present results of ourab initio molecular dynamics simulations on the atomic and electronic structure of clusters of divalent metals, aluminum and antimony, which exhibit a range of bonding characteristics e.g. non-metal-metal transition, metallic and covalent respectively. Results of these studies have been used to develop icosahedral AI12X (X = C, Si and Ge) superatoms with 40 valence electrons which correspond to a filled electronic shell. It is found that the doping leads to a large gain in the binding energy as compared to Al13, suggesting this to be a novel way of developing species for cluster assembled materials. Further studies of adsorption of Li, Si and Cl atoms on Al7 and Al13 clusters show marked variation in the adsorption behaviour of clusters as a function of size and the adsorbate. Silicon reconstructs both the clusters and induces covalency in Al-Al bonds. We discuss the adsorption behaviour in terms of the superatom-atom interactions.
4 citations
Cites background from "Microclusters as superatoms for dev..."
...Since this could lead to a novel way o f developing nanomaterials with desired properties (Kumar 1996; Palmer 1997; Perez et al 1997), much interest has been aroused in understanding the evolution of materials propert ies with size....
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01 Jan 1998
TL;DR: In this article, the authors present results of their studies of adsorption of Li, Na, Mg, Al, Si, P, S and CI atoms on AI7 and AI13 clusters using the ab initio molecular dynamics method.
Abstract: We present results of our studies of adsorption of Li, Na, Mg, Al, Si, P, S and CI atoms on AI7 and AI13 clusters using the ab initio molecular dynamics method. We find a large variation in the binding energy of Li, Na, Mg and CI with the cluster size. In the case of CI on Al7, even the site to site variation in the binding energy is ≈ 1 eV which is much higher than normally found on semi-infinite surfaces. Silicon reconstructs both the clusters and induces covalency in Al-Al bonds. We compare our results with those on Al surfaces and discuss the adsorption behaviour in terms of the superatom-atom interactions where Al7 behaves like an alkali type superatom while, Al13, a halogen.
1 citations
TL;DR: In this paper, the authors present some recent developments in this direction and discuss bonding in such materials, and discuss how to construct new clusters and molecules which could be assembled to form new materials.
Abstract: With the discovery of solid C60, efforts are being made to develop new clusters and molecules which could be assembled to form new materials. Here we present some recent developments in this direction and discuss bonding in such materials.
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TL;DR: In this paper, the Hartree and Hartree-Fock equations are applied to a uniform electron gas, where the exchange and correlation portions of the chemical potential of the gas are used as additional effective potentials.
Abstract: From a theory of Hohenberg and Kohn, approximation methods for treating an inhomogeneous system of interacting electrons are developed. These methods are exact for systems of slowly varying or high density. For the ground state, they lead to self-consistent equations analogous to the Hartree and Hartree-Fock equations, respectively. In these equations the exchange and correlation portions of the chemical potential of a uniform electron gas appear as additional effective potentials. (The exchange portion of our effective potential differs from that due to Slater by a factor of $\frac{2}{3}$.) Electronic systems at finite temperatures and in magnetic fields are also treated by similar methods. An appendix deals with a further correction for systems with short-wavelength density oscillations.
47,477 citations
TL;DR: In this article, the authors proposed a truncated icosahedron, a polygon with 60 vertices and 32 faces, 12 of which are pentagonal and 20 hexagonal.
Abstract: During experiments aimed at understanding the mechanisms by which long-chain carbon molecules are formed in interstellar space and circumstellar shells1, graphite has been vaporized by laser irradiation, producing a remarkably stable cluster consisting of 60 carbon atoms. Concerning the question of what kind of 60-carbon atom structure might give rise to a superstable species, we suggest a truncated icosahedron, a polygon with 60 vertices and 32 faces, 12 of which are pentagonal and 20 hexagonal. This object is commonly encountered as the football shown in Fig. 1. The C60 molecule which results when a carbon atom is placed at each vertex of this structure has all valences satisfied by two single bonds and one double bond, has many resonance structures, and appears to be aromatic. Before 1985, it was generally accepted that elemental carbon exists in two forms, or allotropes: diamond and graphite. Then, Kroto et al. identified the signature of a new, stable form of carbon that consisted of clusters of 60 atoms. They called this third allotrope of carbon 'buckminsterfullerene', and proposed that it consisted of polyhedral molecules in which the atoms were arrayed at the vertices of a truncated icosahedron. In 1990, the synthesis of large quantities of C60 [see Nature 347, 354–358 (1990)] confirmed this hypothesis.
13,394 citations
IBM1
TL;DR: In this paper, Ba−La−Cu−O system, with the composition BaxLa5−xCu5O5(3−y) have been prepared in polycrystalline form, and samples with x=1 and 0.75,y>0, annealed below 900°C under reducing conditions, consist of three phases, one of them a perovskite-like mixed-valent copper compound.
Abstract: Metallic, oxygen-deficient compounds in the Ba−La−Cu−O system, with the composition BaxLa5−xCu5O5(3−y) have been prepared in polycrystalline form. Samples withx=1 and 0.75,y>0, annealed below 900°C under reducing conditions, consist of three phases, one of them a perovskite-like mixed-valent copper compound. Upon cooling, the samples show a linear decrease in resistivity, then an approximately logarithmic increase, interpreted as a beginning of localization. Finally an abrupt decrease by up to three orders of magnitude occurs, reminiscent of the onset of percolative superconductivity. The highest onset temperature is observed in the 30 K range. It is markedly reduced by high current densities. Thus, it results partially from the percolative nature, bute possibly also from 2D superconducting fluctuations of double perovskite layers of one of the phases present.
10,272 citations
"Microclusters as superatoms for dev..." refers background in this paper
...…ones, to prepare new materials with sometimes very surprising properties such as the finding of the solids with non-crystallographic long range orientational order by Shechtman et al (1984) and the exciting discovery of high temperature superconductors (Bednorz and Muller 1986; Wu et a11987)....
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TL;DR: In this article, a new form of pure, solid carbon has been synthesized consisting of a somewhat disordered hexagonal close packing of soccer-ball-shaped C60 molecules.
Abstract: A new form of pure, solid carbon has been synthesized consisting of a somewhat disordered hexagonal close packing of soccer-ball-shaped C60 molecules. Infrared spectra and X-ray diffraction studies of the molecular packing confirm that the molecules have the anticipated 'fullerene' structure. Mass spectroscopy shows that the C70 molecule is present at levels of a few per cent. The solid-state and molecular properties of C60 and its possible role in interstellar space can now be studied in detail.
6,650 citations
TL;DR: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure.
Abstract: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure. An estimated upper critical field H c2(0) between 80 and 180 T was obtained.
5,965 citations