Publications

Reaction of liquid water with Zn and Al powders and foils have been investigated in the 25–75°C range. The reaction of Zn metal powder with water in this temperature range yields ZnO nanorods. The diameter of the nanorods decreases slightly with the increase in the reaction temperature, accompanied by an increase in the relative intensity of UV emission band. Zn metal foils also yield ZnO nanorods on reaction with water in the 25–75°C range. Reaction of Al metal powder or foil with water in the 25–75°C range yields Al(OH)3 nanorods. The formation of ZnO and Al(OH)3 nanorods by the reaction of the metals with water is suggested to occur because of the decomposition of water by the metal giving hydrogen.

Surface oxidation of three metglasses in the Cu-Zr system has been investigated by employing X-ray photoelectron spectroscopy and Auger electron spectroscopy with a view to comparing their oxidation behaviour with that of the corresponding crystalline states of the alloys. Surface oxidation of pure Zr metal has also been examined in detail using these techniques. Sub-oxides of Zr are formed during the initial stages of oxidation of Zr (at oxygen exposures <10L), while at higher exposures, ZrO2 is formed together with the highest possible sub-oxide which the authors designate as 'ZrO'. The relative proportion of 'ZrO' goes through a maximum in the range 25-50 L. Both the glassy and the crystalline states of the Cu-Zr alloys exhibit preferential oxidation of Zr. The glassy alloys exhibit a higher rate of oxidation at intermediate exposures compared with the crystalline states of the alloys; the extent of oxidation at higher oxygen exposures is, however, higher for crystalline alloys. Interatomic Auger transitions have been found in the Zr+O2 system as well as in Cu-Zr alloys.

The enhancement in mechanical and thermal properties of polymer matrices upon reinforcing with nanoparticles strongly depends on the extent of molecular-level interactions and interfacial adhesion between the nanofiller and the matrix material, which are, in turn, governed by the surface functionalities on the nanofiller. Herein, we examine the reinforcing effect of nanosheets of borocarbonitide, (BN)x(C)1-x , which are analogues to graphene (x = 0) and boron nitride sheets (x = 1), whose surface functional groups vary with the composition, on the mechanical and thermal properties of poly(vinyl alcohol), PVA. Results show that substantial improvement in hardness and elastic modulus of PVA is achieved by adding just 0.2 wt% of BCN. A significant enhancement in the thermal stability was also noted. These results are rationalized by recourse to detailed structural characterization, which shows a substantial enhancement in the degree of crystallinity in PVA upon BCN addition, and improved interfacial adhesion between the nanofiller and the polymer matrix via strong intermolecular interactions. Overall, our results show that it is possible to engineer polymer matrix nanocomposites with exceptional mechanical and thermal properties via the addition of a small amount of BCN.

Soak it up: A boron-imidazolate metal–organic framework composed of a mixed ligand system acts as a precursor for the synthesis of a high-surface-area borocarbonitride (BC4N) with remarkable H2 and CO2 storage properties (see figure; ndc=naphthalenedicarboxylate). Furthermore, BC4N has been exploited for the stabilisation of metal (Au and Pd) nanoparticles.

Enthused by the fascinating properties of graphene, we have prepared graphene analogues of BN by a chemical method with a control on the number of layers. The method involves the reaction of boric acid with urea, wherein the relative proportions of the two have been varied over a wide range. Synthesis with a high proportion of urea yields a product with a majority of 1−4 layers. The surface area of BN increases progressively with the decreasing number of layers, and the high surface area BN exhibits high CO2 adsorption, but negligible H2 adsorption. Few-layer BN has been solubilized by interaction with Lewis bases. We have used first-principles simulations to determine structure, phonon dispersion, and elastic properties of BN with planar honeycomb lattice-based n-layer forms. We find that the mechanical stability of BN with respect to out-of-plane deformation is quite different from that of graphene, as evident in the dispersion of their flexural modes. BN is softer than graphene and exhibits signatures of long-range ionic interactions in its optical phonons. Finally, structures with different stacking sequences of BN have comparable energies, suggesting relative abundance of slip faults, stacking faults, and structural inhomogeneities in multilayer BN.

Brillouin scattering measurements have been carried out for the first time on K0.3 MoO3 . The spectrum reveals two bulk modes at 18 and 27 GHz and a Rayleigh surface mode at 6 GHz. Both the bulk modes and the surface mode exhibit changes at the Peierls transition (180 K). Interestingly, the 18 GHz mode also shows softening at the incommensurate-commensurate transition around 100 K, suggesting the important role of phasons.

GaMnN films with 1–3% Mn deposited on Si(100) and Al2O3(0001) substrates, by the technique of nebulized spray pyrolysis by employing acetylacetonate precursors, have been characterized by X-ray diffraction, photoluminescence spectra and other techniques. The films are ferromagnetic and show magnetic hysteresis. The ferromagnetic T C increases with the Mn content, with the 3% Mn film showing a T C of ∼250K. Anomalous Hall effect is observed below T C where the films exhibit a small negative magnetoresistance.

Thin films of ferroelectric PbTiO3(PT) and Pb(Zr0.5 Ti0.5 )O3(PZT) as well as antiferroelectric PbZrO3(PZ) have been prepared on LaNiO3 /SiO2 /Si substrates by nebulized spray pyrolysis (NSP) of metal-organic precursors. The metallic LaNiO3(LNO) electrode layer was also deposited by NSP. The ferroelectric films obtained show satisfactory morphology and desirable dielectric properties. Typical values of the coercive field, remnant polarization and dielectric constant (300 K) for the PT/LNO/SiO2 /Si film are 170 kV cm-1 , 22 µC cm-2and 210, respectively, with the corresponding values for the PZT/LNO/SiO2 /Si film being 120 kV cm-1 , 13 µC cm-2and 540, respectively. The PZ/LNO/SiO2 /Si film shows typical antiferroelectric characteristics including the electric-field induced reversible antiferroelectric - ferroelectric transition. The various films deposited on LNO/SiO2 /Si by NSP are comparable in all respects to those prepared on Pt/Ti/SiO2 /Si by the same technique.

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