Publications

Members of the YFe1−x Mn x O3 (0≤x≤0.45) family crystallize in the GdFeO3 type orthorhombic perovskite structure (space group Pnma) where the Fe and Mn ions are disordered at the 4b crystallographic site. Upon substitution of Mn at the Fe-site in the canted antiferromagnetic YFeO3 (T N=640K), a first-order spin-reorientation transition occurs at a temperature, T SR, where the magnetic structure changes from the canted to a collinear state. With increasing Mn-concentration, T SR increases whereas T N decreases. Neutron diffraction studies on the x=0.4 sample reveal that the spin structure changes from Γ 4 to Γ 1 below T SR. Intriguingly, when x=0.4 and 0.45, a temperature-induced magnetization reversal is observed below a compensation temperature T ⁎ (T ⁎<T SR<T N). The reversal is explained on the basis of a ferrimagnetic ground state resulting from antiferromagnetic coupling of the canted moments of Fe–O–Fe and Mn–O–Mn with that of Fe–O–Mn ordering.

A green and facile approach has been developed for the large-scale synthesis of nanosheets of reduced graphene oxide (rGO) and nitrogenated reduced graphene oxide (N-rGO). This has been achieved by direct thermal decomposition of sucrose and glycine at 475 °C in ca. 7 minutes, respectively. The present protocols for synthesizing rGO and N-rGO are simple and environmentally friendly as we do not use any harmful reagents, metal catalysts and solvents. Along with that, this method offers an inexpensive route with high yields to prepare rGO with a high nitrogen content (20-25 atom %). To further improve the properties of the synthesized rGO sheets, hydrogen treatment has been carried out to reduce the oxygen functional groups. Cyclic voltammograms and charge-discharge experiments have been carried out to understand the supercapacitor behavior of rGO and hydrogen treated (H-rGO) samples.

No abstract is provided for this article.

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.

We present experimental measurements and first‐principles theoretical analysis of high‐temperature electron‐transport properties of polycrystalline Te‐deficient 2H‐ and 1T′‐MoTe 2– x . Electron transport measurements in the temperature range 300–673 K show that polycrystalline 2H‐MoTe 2– x exhibits two regimes of activated conduction: hopping of defect‐induced localized carriers at lower temperatures and an extended state conduction at higher temperatures. Its Seebeck coefficient changes from p‐type to n‐type around 497 K peaking near 370 K, which is ascribed to mixed conduction of carriers. In contrast, 1T′‐MoTe 2– x exhibits metallic conduction up to 300 K beyond which conductivity slightly increases due to thermal excitation of the minority carriers. 2H‐ and 1T′ forms of MoTe 2– x exhibit thermal conductivity with opposite temperature‐dependence due to dominant electronic thermal conductivity in the latter. Using first‐principles calculations based on density functional theory, we determine the nature of defect states associated with Te‐vacancies in 2H‐, 1T′‐ and Td‐MoTe 2– x . The defect bands associated with Te vacancies appear within the gap of 2H‐MoTe 2 and in the pseudo gap of 1T′‐MoTe 2 , thereby reducing the bandgap of the former and making the latter more metallic. These defect states are crucial to understanding the observed trends in the temperature‐dependent transport properties of Te‐deficient 2H‐ and 1T′‐MoTe 2– x .

Nanosheets containing few-layers of ferroelectric Aurivillius family of oxides, Bi2 A n−1 B n O3n+3 (where A=Bi3+, Ba2+ etc. and B=Ti4+, Fe3+ etc.) with n=3, 4, 5, 6 and 7 have been prepared by reaction with n-butyllithium, followed by exfoliation in water. The few-layer samples have been characterized by Tyndall cones, atomic force microscopy, optical spectroscopy and other techniques. The few-layer species have a thickness corresponding to a fraction of the c-parameter along which axis the perovskite layers are stacked. Magnetization measurements have been carried out on the few-layer samples containing iron. Few-layer species of a few layered metal-organic compounds have been obtained by ultrasonication and characterized by Tyndall cones, atomic force microscopy, optical spectroscopy and magnetic measurements. Significant changes in the optical spectra and magnetic properties are found in the few-layer species compared to the bulk samples. Few-layer species of the Aurivillius family of oxides may find uses as thin layer dielectrics in photovoltaics and other applications.

One of the applications of nanomaterials is as reinforcements in composites, wherein small additions of nanomaterials lead to large enhancements in mechanical properties. There have been extensive studies in the literature on composites where a polymer matrix is reinforced by a single nanomaterial such as carbon nanotubes. In this article, we examine the significant synergistic effects observed when 2 different types of nanocarbons are incorporated in a polymer matrix. Thus, binary combinations of nanodiamond, few-layer graphene, and single-walled nanotubes have been used to reinforce polyvinyl alcohol. The mechanical properties of the resulting composites, evaluated by the nanoindentation technique, show extraordinary synergy, improving the stiffness and hardness by as much as 400% compared to those obtained with single nanocarbon reinforcements. These results suggest a way of designing advanced materials with extraordinary mechanical properties by incorporating small amounts of 2 nanomaterials such as graphene plus nanodiamond or nanodiamond plus carbon nanotube.