Publications

Nanoparticles of MnO with average diameters in the 6–14 nm range have been prepared by the decomposition of manganese cupferronate in the presence of TOPO, under solvothermal conditions. Nanoparticles of NiO with average diameters in the 3–24 nm range have been prepared by the decomposition of nickel cupferronate or acetate under solvothermal conditions. The nanoparticles have been characterized by X-ray diffraction and transmission electron microscopy. Both MnO and NiO nanoparticles exhibit supermagnetism, accompanied by magnetic hysteresis below the blocking temperature (TB). The TB increases with the increase in particle size in the case of NiO, and exhibits the reverse trend in the case of MnO.

In the systematic study of amine … LiCl [amines = NH3, CH3NH2, (CH3)2NH] complexes the possibility of an ion-pair structure and the effect of methylation on the stabilization energy is investigated. ΔEis evaluated by the SCF/4-31G method and augmented by the approximate dispersion energy calculated perturbationally. The interaction energy decreases with the increasing number of methyl groups in the amine. The dispersion energy plays a negligible role in the stabilization of complexes. None of the systems studied are ion pairs; their Li bonds are of a so-called molecular type. Due to the divergence of the multipole expansion, the attempt to correct the 4-31G stabilization energies via the electrostatic energy fails. The relative order of the ΔE in the series of complexes is verified instead in the extended basis set calculation. The lithium bonds are compared with their H-bonded analogues.

A new analogue of graphene containing boron, carbon and nitrogen (BCN) has been obtained by the reaction of high-surface-area activated charcoal with a mixture of boric acid and urea at 900 degrees C. X-ray photoelectron spectroscopy and electron energy-loss spectroscopy reveal the composition to be close to BCN. The X-ray diffraction pattern, high-resolution electron microscopy images and Raman spectrum indicate the presence of graphite-type layers with low sheet-to-sheet registry. Atomic force microscopy reveals the sample to consist of two to three layers of BCN, as in a few-layer graphene. BCN exhibits more electrical resistivity than graphene, but weaker magnetic features. BCN exhibits a surface area of 2911 m(2) g(-1), which is the highest value known for a B(x)C(y)N(z) composition. It exhibits high propensity for adsorbing CO(2) ( approximately 100 wt %) at 195 K and a hydrogen uptake of 2.6 wt % at 77 K. A first-principles pseudopotential-based DFT study shows the stable structure to consist of BN(3) and NB(3) motifs. The calculations also suggest the strongest CO(2) adsorption to occur with a binding energy of 3.7 kJ mol(-1) compared with 2.0 kJ mol(-1) on graphene.

Performance of supercapacitors based on 1:1 (by weight) composites of polyaniline (PANI) with nanosheets of nitrogenated reduced graphene oxide (NRGO), BC1.5N, MoS2 and WS2 has been investigated in detail. The highest specific capacitance is found with the 1:1 NRGO-PANI composite, the value being 561F/g at a current density of 0.2A/g. All the 1:1 nanocomposites show good cyclability. Increasing the PANI content increases the specific capacitance and the highest value found being 715F/g at a current density of 0.5A/g in the case of the 1:6 NRGO-PANI composite. However, all the 1:6 composites show a marked decrease in specific capacitance with increase in current density. The energy density of 1:6 NRGO-PANI is ~25Wh/Kg at 0.5A/g and 1:1 NRGO-PANI is ~19Wh/Kg at 0.2A/g. NRGO-PANI composites clearly stand out as viable materials for practical applications.

Boron-doped carbon nanotubes have been prepared by the pyrolysis of acetylene–diborane mixtures in a stream of helium and hydrogen. The nanotubes so obtained have compositions around C35B. The presence of boron favours nanotube formation and the boron content does not vary with the depth. Considering that the nitrogen-doped nanotubes, reported recently (Chem. Phys. Lett. 287 (1997) 671) have the average composition C35N, it may be possible to use a combination of these p-type and n-type nanotubes for certain applications.

YCrO3, which has a monoclinic structure, shows weak ferromagnetism below 140 K (TN) and a ferroelectric transition at 473 K accompanied by hysteresis. We have determined the structure and energetics of YCrO3 with ferromagnetic and antiferromagnetic ordering by means of first-principles density functional theory calculations, based on pseudopotentials and a plane-wave basis. The noncentrosymmetric monoclinic structure is found to be lower in energy than the orthorhombic structure, supporting the biferroic nature of YCrO3.

Interaction of two different samples of graphene with DNA nucleobases and nucleosides is investigated by isothermal titration calorimetry. The relative interaction energies of the nucleobases decrease in the order guanine (G)>adenine (A)>cytosine (C)>thymine (T) in aqueous solutions, although the positions of C and T seem to be interchangeable. The same trend is found with the nucleosides. Interaction energies of the A-T and G-C pairs are somewhere between those of the constituent bases. Theoretical calculations including van der Waals interaction and solvation energies give the trend G>A approximately T>C. The magnitudes of the interaction energies of the nucleobases with graphene are similar to those found with single-walled carbon nanotubes.

Structure and superconducting properties of Tl1−y Pb y Y1−x Ca x Sr2Cu2O7 (y=0.0, 0.1, 0.25 and 0.5) , derived from the parent insulator TlYSr2Cu2O7, have been investigated for different values of x. XANES studies show Pb to be in the 4+ state while Tl is in the 3+ state, suggesting thereby that in this series, (x−y) approximately corresponds to the hole concentration. The in-plane CuO distance decreases with increase in x for all values of y. The apical CuO distance as well as the Tl(Pb)O(2) distance show anomalies at x=0.5 in the series with y=0.25; at this composition, T c also reaches a maximum. In general, the composition (value of x) at which the T c of Tl1−y Pb y Y1−x Ca x Sr2Cu2O7 reaches a maximum depends on the Pb content and the maximum T c itself increases with increase in y, reaching a value of 105 K at y=0.5. More interestingly, a maximum T c occurs at an (x−y) value of ∼0.25, which is close to the hole concentration at maximum T c in other cuprate superconductors containing two CuO2 layers.

YMnO3 thin films have been grown on n ‐ type Si substrates by nebulized spray pyrolysis in the Metal ‐ Ferroelectric ‐ Semiconductor (MFS) configuration. The C-V characteristics of the film in MFS structure exhibit hysteretic behavior consistent with the polarization charge switching direction, with the memory window decreasing with increase in temperature. The density of interface states decreases with the increase in the annealing temperature. Mapping of the silicon energy band gap with the interface states has been carried out. The leakage current measured in the accumulation region, is lower in well-crystallized thin films and obeys a space- charge limited conduction mechanism.

Various methods have been employed to prepare nanostructured GaN exhibiting reasonable surface areas. The methods include ammonolysis of γ-Ga2O3 or Ga2O3 prepared in the presence of a surfactant, and the reaction of a mixture of Ga2O3 and Ga(acac)3 with NH3. The latter reaction was also carried out in the presence of H3BO3. All the methods yield good GaN samples as characterized by X-ray diffraction, electron microscopy and photoluminescence measurements. Relatively high surface areas were obtained with the GaN samples prepared by the ammonolysis of γ-Ga2O3 (53 m2 g−1), and of Ga2O3 prepared in the presence of a surfactant (66 m2 g−1). GaN obtained by the reaction of NH3 with a mixture of Ga2O3, Ga(acac)3 and boric acid gave a surface area of 59 m2 g−1. GaN nanoparticles prepared by the nitridation of mesoporous Ga2O3 samples generally retain some porosity.