Publications

C60·TDAE = tetrakis(dimethylamino)ethylene) with a Tc of ∼ 16K is probably the best example of an organic molecular ferromagnet known to date. Based on ESR studies, we demonstrate that C60·TDAE is a quasi one-dimensional spin one-half Heisenberg ferromagnet, with the C60 units being entirely responsible for the magnetism. C60-C60 interactions responsible for superconductivity in alkali metal doped C60 seem to be essential for the magnetism of C60·TDAE as well.

Dehydration of Mo1 –xWxO3· H2O (0 ⩽x⩽ 1.0) gives rise to oxides of 'ReO3' structure, the 'ReO3' structure transforming to the layered structure in the case of MoO3; reduced Mo1 –xWxO3 samples exhibit disordered {102} shear planes.

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.

Development of inexpensive and efficient photo- and electro-catalysts is vital for clean energy applications.

Phosphorenes functionalized with InCl₃, B(C₆F₅)₃ and a benzyl group show good ambient stability and high photocatalytic HER activity.

Gold nanoparticles with average diameters in the range 2.5-15 nm, prepared at the organic/aqueous interface by using tetrakis(hydroxymethyl)phosphonium chloride (THPC) as reducing agent, exhibit ferromagnetism whereby the saturation magnetization M(S) increases with decreasing diameter and varies linearly with the fraction of surface atoms. The value of M(S) is higher when the particles are present as a film instead of as a sol. Capping with strongly interacting ligands such as alkane thiols results in a higher M(S) value, which varies with the strength of the metal-sulfur bond. Ferromagnetism is also found in Pt and Ag nanoparticles prepared as sols, and the M(S) values vary as Pt>Au>Ag. A careful study of the temperature variation of the magnetization of Au nanoparticles, along with certain other observations, suggests that small bare nanoparticles of noble metals could indeed possess ferromagnetism, albeit weak, which is accentuated in the presence of capping agents, specially alkane thiols which form strong metal-sulfur bonds.

Noting that BiI3 and the well-known topological insulator (TI) Bi2Se3 have the same high symmetry parent structures, and that it is desirable to find a wide-band gap TI, we determine here the effects of pressure on the structure, phonons and electronic properties of rhombohedral BiI3. We report a pressure-induced insulator-metal transition near 1.5 GPa, using high pressure electrical resistivity and Raman measurements. X-ray diffraction studies, as a function of pressure, reveal a structural peculiarity of the BiI3 crystal, with a drastic drop in c/a ratio at 1.5 GPa, and a structural phase transition from rhombohedral to monoclinic structure at 8.8 GPa. Interestingly, the metallic phase, at relatively low pressures, exhibits minimal resistivity at low temperatures, similar to that in Bi2Se3. We corroborate these findings with first-principles calculations and suggest that the drop in the resistivity of BiI3 in the 1–3 GPa range of pressure arises possibly from the appearance of an intermediate crystal phase with a lower band-gap and hexagonal crystal structure. Calculated Born effective charges reveal the presence of metallic states in the structural vicinity of rhombohedral BiI3. Changes in the topology of the electronic bands of BiI3 with pressure, and a sharp decrease in the c/a ratio below 2 GPa, are shown to give rise to changes in the slope of phonon frequencies near that pressure.

Sensing characteristics of few-layer graphenes for NO2 and humidity have been investigated with graphene samples prepared by the thermal exfoliation of graphitic oxide, conversion of nanodiamond (DG) and arc-discharge of graphite in hydrogen (HG). The sensitivity for NO2 is found to be highest with DG. Nitrogen-doped HG (n-type) shows increased sensitivity for NO2 compared with pure HG. The highest sensitivity for humidity is observed with HG. Sensing characteristics of graphene have been examined for different aliphatic alcohols and the sensitivity is found to vary with the chain length and branching.

The effect of the thermally induced spin-state transition on the phonon mode behavior of LaCoO3 has been investigated by using Raman spectroscopy. The number of observed Raman modes is larger than the number predicted by group theory for a rhombohedrally distorted perovskite structure with the space group R 3 ̄ c. There is a strong similarity between the Raman spectrum of LaCoO3 and LaMnO3 at ambient conditions due to the Jahn–Teller (J–T) distortion associated with the intermediate-spin (IS) state of Co3+. The J–T distortion splits the external mode associated with La–O vibration into a doublet above the spin-state transition temperature. There is an increase in the anharmonic coupling between the one-phonon states with increase in temperature above the transition temperature, due to the gradual increase in the population of Co3+ in the IS state.