Publications

Following the theoretical predictions of ferromagnetism in Mn- and Co-doped ZnO, several workers reported ferromagnetism in thin films as well as in bulk samples of these materials. While some observe room-temperature ferromagnetism, others find magnetization at low temperatures. Some of the reports, however, cast considerable doubt on the magnetism of Mn- and Co-doped ZnO. In order to conclusively establish the properties of Mn- and Co-doped ZnO, samples with 6% and 2% dopant concentrations have been prepared by the low-temperature decomposition of acetate solid solutions. The samples have been characterized by X-ray diffraction, EDAX and spectroscopic methods to ensure that the dopants are substitutional. All the Mn- and Co-doped ZnO samples (prepared at 400 °C and 500 °C) fail to show ferromagnetism. Instead, their magnetic properties are best described by a Curie–Weiss type behavior. It appears unlikely that these materials would be useful for spintronics, unless additional carriers are introduced by some means.

Normal coordinate analyses of N, N′-dimethylurea and tetramethylurea were carried out employing a Urey-Bradley force field. The majority of the bands observed in the infrared spectra of alkylurea derivatives arise from mixed vibrations just as in secondary amides. Dialkylureas show evidence for the presence of rotamers with NH bonds cis and trans with respect to the carbonyl oxygen. The perturbations of the mixed vibration bands of alkylureas in charge-transfer as well as metal complexes are discussed.

A three-dimensional open-framework tin(II) phosphate, prepared hydrothermally with 1,3-diaminopentane as the template, is shown to exhibit reversible dehydration and ion-exchange properties. In celebration of Tony Cheetham's 70th birthday

Although it is believed that there is strong hybridization between the Cu(3d) and O(2p) orbitals in the layered cuprates and that the parent compounds such as La2CuO4 are charge-transfer gap insulators, very few models consider the CuO charge-transfer energy, Δ, or the hybridization strength, tpd, to be the important factors responsible for the superconductivity of these materials. Based on the crucial experimental observation that the relative intensity of the features in Cu(2p) photoemission of several families of cuprates varies systematically with the hole concentration, nh, we have been able to show that both these properties vary smoothly with Δ /tpd. More importantly, we show that the electronic polarizability of the CuO2 sheets, α , is sufficiently large to favour hole pairing and that the value α also depends on Δ/tpd. Both nh and α increase smoothly with decreasing Δ /tpd. Considering that the maximum Tc in the various cuprate families containing the same number of CuO2 sheets occurs around the same nh value (e.g., nh≈ 0.2 in cuprates with two CuO2 sheets). The present study demonstrates how Δ /tpd, α and such chemical bonding characteristics have an important bearing on the superconducting properties of the cuprates.

Quasi-two-dimensional oxides of the La1−x Sr1+x MnO4 system, possessing the K2NiF4 structure, show no evidence for ferromagnetic ordering in contrast to the corresponding three-dimensional La1−x Sr x MnO3 perovskites. Instead, there is an increasing tendency toward antiferromagnetic ordering with increasingx in La1−x Sr1+x MnO4. Furthermore, these oxides are relatively high-resistivity materials over the entire compositional range. Substitution of Ba for Sr in La0.5Sr1.5MnO4 decreases the ferromagnetic interaction. Increasing the number of perovskite layers in SrO · (La1−x Sr x MnO3) n causes an increase in electrical conductivity as well as ferromagnetic interaction. The oxide becomes a highly conducting ferromagnet whenn ≥ 2.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Multiwalled as well as single-walled carbon nanotubes are conveniently prepared by the pyrolysis of organometallic precursors such as metallocenes and phthalocyanines in a reducing atmosphere. More importantly, pyrolysis of organometallics alone or in mixture with hydrocarbons yields aligned nanotube bundles with useful field emission and hydrogen storage properties. By pyrolysis of organometallics in the presence of thiophene, Y-junction nanotubes are obtained in large quantities. The Y-junction tubes have a good potential in nanoelectronics. Carbon nanotubes prepared from organometallics are useful to prepare nanowires and nanotubes of other materials such as BN, GaN, SiC, and Si3N4.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Covalent functionalization of nanowires of TiO2, ZnO and Al2O3 has been carried out by employing the organosilicon reagents aminopropyltriethoxysilane and hexadecyltrimethoxysilane (HDTMS). The presence of the organosilane coating was confirmed by electron microscopy, energy dispersive X-ray analysis (EDXA) and IR spectroscopy. HDTMS-coated oxide nanowires give stable dispersions in CCl4 and toluene. Nanoparticles of these metal oxides as well as of CeO2 and Fe3O4 could be solubilized in non-polar solvents by functionalizing with HDTMS. Nanotubes and nanoparticles of BN could also be functionalized and solubilized with HDTMS. Organotin reagents have also been used to covalently functionalize oxide nanostructures and multi-walled carbon nanotubes, thereby producing stable dispersions in CCl4 and toluene. The organotin reagents used were dibutyldimethoxytin and trioctyltinchloride. Covalent functionalization of nanostructures using organosilane and organotin reagents provides a general method applicable to large class of inorganic materials as well as carbon nanotubes and is likely to be useful in practice.

Monte Carlo calculations on liquid and glassy isopentane have been performed by using transferable intermolecular potential functions (t. i. ps). Thermodynamic properties, radial distribution functions, coordination number distributions, etc., calculated for the liquid are in reasonable agreement with the experimental values. By quenching the liquid, we have obtained the glass-transition temperature from the temperature variation of intermolecular energy, volume and the heat of vaporization. Radial distribution functions suggest a structure of the glass primarily influenced by geometrical factors and with no preference for any particular orientation ; the peak around 4.0 Å (1 Å = 10 -10 m = 10 -1 nm) between the more exposed carbon atoms seems to be the characteristic of densely packed hydrocarbons. The histogram of the nearest-neighbour distribution shows a shift towards higher coordination in the glassy state. Interesting differences are found between the liquid and the glass in the dimerization energy and bonding energy distribution functions. Narrower distribution is found on vitrification in the dihedral angle distribution function for rotation around the central C–C bond.

The detailed electronic structure of the n–v addition compound H2O⋅BF3 has been investigated for the first time by a combined use of electron energy loss spectroscopy (EELS) and UV photoelectron spectroscopy (UPS) augmented by MO calculations. The calculated molecular orbital energies of H2O⋅BF3 agree well with the UPS results and have been used to assign the electronic transitions obtained from EELS and to construct an orbital correlation diagram.