Publications

The Metal–Nonmetal Transition: A Global Perspective

No abstract is provided for this article.

Multiferroic and magnetoelectric properties of core-shell CoFe2O4@BaTiO3 nanocomposites

Core-shell CoFe2O4@BaTiO3 nanoparticles and nanotubes have been prepared using a combination of solution processing and high temperature calcination. Both the core-shell nanostructures exhibit magnetic and dielectric hysteresis at room temperature and magnetoelectric effect. The dielectric constant of both the nanocomposites decreases upon application of magnetic field. The core-shell nanoparticles exhibit 1.7% change in magnetocapacitance around 134 K at 1 T, while the core-shell nanotubes show a remarkable 4.5% change in magnetocapacitance around 310 K at 2 T.

Infrared spectra of acid azides, carbamyl azides and other azido derivatives

The infrared spectra of organic acid azides, carbamyl azides, vinyl azides and alphaazido ethers, thioethers and amines have been investigated in detail. The acid azides and the carbamyl azides show the characteristic N3 and carbonyl absorptions and have been assigned the acyclic azide structure. The amide bands of carbamyl azides have also been assigned. The asymmetric and symmetric stretching frequencies of the azido group are generally found in the regions 2162–2095 and 1258–1206 cm−1, respectively. The anomalous splittings of the N3 stretching bands have been explained in terms of Fermi interaction with combination tones involving the N3 symmetric and C-N stretching vibrations and other low lying frequencies.

Computer simulation of glasses

Monte Carlo and molecular dynamics computer simulation methods were used to model glass structure with emphasis on the structure at temperatures around the glass transition temperature. Reliable intermolecular potentials were used to obtain results on glasses formed by isopentane, water, and MeOH.

Synthesis and Structural Characterization of a Chiral Open-Framework Tin(II) Phosphate, [CN₃H₆][Sn₄P₃O₁₂] (GUAN−SnPO)

A chiral open-framework tin phosphate structure, [CN3H6][Sn4P3O12], has been obtained by using an achiral structure-directing agent, guanidine. The structures of both enantiomorphs have been determined: tetragonal, space groups P43 (No. 78) and P41 (No. 76), a = 8.8881(1) Å, c = 20.6029(4) Å, V = 1627.59 (4) Å3, Z = 4, M = 819.76. The framework, which is composed of puckered 6-membered (Sn3P3O6) and 12-membered (Sn6P6O12) rings, accommodates the organic cation in a tortuous chiral channel.

ChemInform Abstract: Electronic Structures of H2O·BF3 and Related n‐v Addition Compounds: A Combined EELS‐UPS Study in Vapor Phase

Structural Evolution and Electronic Properties of La_1+<i>x</i>Sr_2-<i>x</i>Mn₂O₇

A detailed study of the layered manganite La1+xSr2-xMn2O7 has been performed, establishing that within the composition range 0.1 ≤ x ≤ 0.45 the phases crystallize in the I4/mmm space group. The evolution of structural parameters with x in this composition range has been followed using a novel application of an existing program for the Rietveld analysis of powder diffraction data. The structure, a familiar intergrowth of rock-salt (La,Sr)O slabs and double perovskite (La,Sr)2Mn2O6 units, is characterized by a reluctance to deform the latter. This manifests as a "pumping" of the larger SrII ion into the 12-coordinate site of the structure as x is increased. We report these features of the structure as well as electrical transport and magnetic properties, in light of recent observations of giant, negative magnetoresistance in these systems.

A new criterion for the metallicity of elements

A vast majority of elements are metallic in the liquid state. The latent heat of vapourization, ΔHv, of such elements is greater than the critical value of ∼ 42 kJ mol−1 (0.44 eV mol−) which demarcates metals from non-metals. It is shown that ΔHv can be related to the Fermi energy as well as to the Herzfeld criterion involving atomic polarizability.

Anderson transitions in Ln 1-x Sr x CoO 3 (Ln=Pr or Nd)

Electrical conductivity measurements show that Ln 1−x Sr x CoO 3 , (Ln = Pr or Nd) undergoes a non-metal-metal transition when x≈0 3. The d.c. conductivity of compositions with 0<x<0.l obeys the T −1/4 law up to 400 K and the a.c. conductivity data follow the ω δ law with δ in the range 0.6-0.8. Surprisingly, however, δ seems to increase with increasing temperature. Thermopower measurements show clear evidence for a change in the mechanism of conduction (around 350 K) from variable range hopping to transport at E c . All these transport properties suggest that Co 4+ ions in Ln 1-x Sr x CoO 3 (0<x<0.1), considered as moving in a lattice of Co 3+ , form a degenerate gas and that the states at the Fermi energy are Anderson localized.

CCDC 224288: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Nanomaterials Chemistry: Recent Developments and New Directions

No abstract is provided for this article.

Systematic Organic UV Photoelectron Spectroscopy

Photoelectron spectroscopy (PES) provides valuable information on the ionization energies of atoms and molecules. The ionization energy (IE) is given by the relation. hv = IE + T where hv is t h e energy of the radiation and T i s the kinetic energy of the electron. The IEs are directly related to the orbital energies (Koopmans' theorem). By employing UV radiation (HeI. 21.2 eV. or HeII. 40.8 eV). extensive data on the ionization of valence electrons in organic molecules have been obtained in recent years. These studies of UV photoelectron spectroscopy. originated by Turner, have provided a direct probe into the energy levels of organic molecules. Molecular orbital calculations of various degrees of sophistication are generally employed to make assignments of the PES bands. Analysis of the vibrational structure of PES bands has not only provided structural information on the molecular ions, but has also been of value in band assignments. Dewar and co-workers [1, 2) presented summaries of available PES data on organic molecules in 1969 and 1970. Turner et al. [3] published a handbook of Hel spectra of organic molecules in 1970. Since then, a few books [4-7] discussing the principles and applications of UV photoelectron spectroscopy have appeared of which special mention should be made of the recent article by Heilbronner and Maier [7]. There has, however, been no comprehensive review of the vast amount of data on the UV-PES of organic molecules published in the literature since 1970.

An infrared spectroscopic study of the phase transitions of crystalline aromatic donor—acceptor complexes involving a pseudoplastic state

Variable temperature i.r. spectroscopic studies of weak π-donor-π-acceptor complexes in the crystalline state indicate that the complexes undergo order—disorder transitions, the disorder being caused by molecular motion. Thermodynamic data on the phase transitions along with the spectral data suggest that the high-temperature crystalline forms of the complexes are likely to be pseudoplastic.

Computer simulation of transformations in solids

Recent developments in molecular dynamics (MD) and Monte Carlo (MC) methods enable us to fruitfully investigate transformations in solids by employing appropriate potentials. The possibility of varying both the volume and the shape of the simulation cell in these simulation techniques is especially noteworthy. In this article we briefly describe some of the highlights of the recent MD and MC methods and show how they are useful in the study of transitions in monatomic solids, ionic solids, molecular solids (especially orientationally disordered solids), and glasses. The availability of reliable pair potentials will undoubtedly make these methods more and more useful for studying various aspects of condensed matter in the years to come.

An ultraviolet photoelectron spectroscopic study of BF3–donor complexes

He i spectra of strong n–v type adducts of BF3 with H2O, CH3OH, (C2H5)2O, and CH3CN as well as of weak complexes of BF3 with NO and H2S are reported along with assignments based on MO calculations. The energy of the fluorine orbitals of BF3 is shown to be shifted in proportion to the strength of the donor–acceptor interaction. BF3 seems to form a contact pair with CS2.

Relation between high-tc superconductivity and structure - a study of la3-xba3+xcu6o14+delta and yba2cu3o7-delta systems

Superconductivity is found in tetragonal La3−x Ba3+x Cu6O14+δ and La, Ba)6−x Sr x Cu6O14+δ even though they do not possess Cu-O chains or the K2NiF4 structure. Resistivity measurements confirm the occurrence of a transformation from chain-superconductivity to sheet-superconductivity in YBa2Cu3O7−δ as δ is varied in the range 0.0–0.5.&#13;\n

Loop based pseudo hamming values—I testing isomorphism and rating kinematic chains

Topology of kinematic chains is useful in comparing them from the structural-error point of view and an attempt was made by one of the authors in this direction. The method reported, however, fails to compare the chains which consist of the same number and type of links and joints, ternary-binary, ternary-quaternary, etc. but differ in loop formation only. The present paper supplements the earlier work and makes it complete. Further, comparison of the loop Hamming values of links and chains is expected to be the simplest and positive test for isomorphism. A note on the type of freedom is also included.

Electronic Structures of Perovskite Oxides of Transition Metals of the Type LaMO3 (M = Ti-Ni) as Revealed by MSXα Investigations

Systematic investigations of the electronic structures of MO9- 6 (M = Ti-Ni) clusters, as in the LaMO3 type perovskite oxides, have been carried out by employing the multiple-scattering Xα (MSXα) method. The crystal-field splitting of the metal d level is found to increase, while the oxygen-to-metal charge-transfer energy decreases across the transition metal series. Systematic trends are also seen in the mixing (covalency) between the metal d and the oxygen 2p orbitals in the series.