2,089 publications from this institution
Nanoparticles probably constitute the largest class of nanomaterials. Nanoparticles of several inorganic materials have been prepared by employing a variety of synthetic strategies. Besides synthesizing nanoparticles, there has been considerable effort to selectively prepare nanoparticles of different shapes. In view of the great interest in inorganic nanoparticles evinced in the last few years, we have prepared this perspective on the present status of the synthesis of inorganic nanoparticles. This article includes a brief discussion of methods followed by reports on the synthesis of nanoparticles of various classes of inorganic materials such as metals, alloys, oxides chalcogenides and pnictides. A brief section on core–shell nanoparticles is also included.
New cluster species of the type (HCN) m (NH3) n H+ with m up to 4 and n up to 7 alongwith (NH3) n H+ species are observed using mass spectrometry, on the reaction of carbon vapor with jet-cooled NH3 in admixture with helium. The most preponderant species correspond to m=1 and 2, viz. (HCN)1(NH3)4H+, (HCN)1(NH3)3H+ and (HCN)2(NH3)3H+. These clusters involving the tetrahedral coordination in the first solvation shell of the NH4 + ion are the most stable species, as corroborated by molecular-orbital calculations. The incremental complexation energy due to successive addition of the NH3 molecule to (HCN)(NH3) n H+, decreases monotonically with increasing n, for n>2.
No abstract is provided for this article.
Electron energy loss spectroscopy (EELS) has been employed to monitor surface conductivity changes in YBa2Cu3O7 as a function of temperature. Concomitant use of x-ray photoelectron spectroscopy (XPS) establishes that the formation of oxygen dimers with lowering of temperature is accompanied by a simultaneous increase of surface conductivity.
Nanoparticles of metals such as Au, Ag, Pd and Pt embedded in exfoliated sheets of aminoclays of the type R8Si8Mg6O16(OH)4, where R = CH2CH2NH2 are entirely water soluble. These sheets of the composite come to the organic-aqueous interface on addition of alkane thiols to the aqueous layer.
La2−xSrxNiO4 shows a maximum in the c / a ratio around x = 0.6 up to which composition the concentration of holes is equal to that expected theoretically. The material becomes a degenerate semiconductor above a certain temperature up to x = 0.8, but is metallic at room temperature when x ⩾ 1.0. All the compositions with x ⩾ 0.05 are paramagnetic in the 15 - 300K range. Based on these measurements, an electronic phase diagram is tentatively proposed. It is noteworthy that the antiferromagnetic order disappears at low doping levels in both La2−xSrxNiO4 and La2−xSrxCuO4, but metallicity is seen at 300K only at a much higher x value in the former system.
For Abstract see ChemInform Abstract in Full Text.
Two new open-framework yttrium oxalates have been prepared, for the first time, employing hydrothermal methods in the presence of organic amines. The crystal data for these oxalates are as follows: I, [C6N2H16]0.5[Y(H2O)(C2O4)2]·2H2O, triclinic, space group P(−1) (no. 2), a = 8.229(3), b = 9.739(1), c = 9.754(3) Å, α = 60.74(1), β = 72.36(1), γ = 84.67(1)°, V = 648.5(1) Å3, Z = 2, M = 377.1, Dcalc = 1.931 g cm-3, μ = 4.554 mm-1, Mo Kα, R1 = 0.054, wR2 = 0.13; II, [C5N2H12][Y(C2O4)2], monoclinic, space group Cc (no. 9), a = 11.552(1), b = 17.168(1), c = 8.719(1) Å, β = 130.64(1)°, V = 1312.1(1) Å3, Z = 2, M = 365.1, Dcalc = 1.848 g cm-3, μ = 4.48 mm-1, Mo Kα, R1 = 0.023, wR2 = 0.057. The Y atom is 9-coordinated in I, forming a D3h triply capped trigonal prism, and 8-coordinated in II, forming a square antiprism. The three-dimensional framework structures of I and II are built up by in-plane linkages between the Y and the oxalate moieties, forming layers with 12-membered honeycomb-like apertures, pillared by another oxalate in an out-of-plane manner. While I possesses channels along all the crystallographic directions, II has channels only in one direction. Adsorption studies indicate that water and methanol can be reversibly adsorbed in I.
The effect of Mn substitution on the multiferroic properties of Y CrO3 and LuCrO3 has been investigated. Solid solutions of the type Y Cr1−x Mn x O3 and LuCr1−x Mn x O3 ( x = 0.0 – 0.3 ) possess orthorhombic structures with Pnma and Pbnm space groups respectively. Both the series of materials show canted antiferromagnetic behavior with T N decreasing with increasing x . They also exhibit ferroelectricity with the transition temperature decreasing with increases in x . The x = 0.3 compositions show improved magnetic properties with a ferroelectric transition in the 418–425 K range.
Electronic properties of oxide perovskites are briefly presented with special reference to quasi two-dimensional oxides of K2NiF4 structure. Structure and properties of the various families of cuprate superconductors containing perovskite layers are discussed in some detail, primarily based on the work carried out in the author's laboratory. The nature of Cu and oxygen in the cuprates is examined and the role of oxygen holes indicated. Oxygen holes seem to be present in many other perovskite oxides as well. The recently discovered electron-superconductivity in cuprates is presented as also the unusual dielectric properties of bismuth cuprate glasses. Scope for further investigations and possible future directions are indicated.
No abstract is provided for this article.
Borocarbonitrides, (BN)1–x(C)x, provide a means of composition-tuning the bandgap of BN and graphene. (BN)1–x(C)x thin films of varied chemical compositions have been deposited on c-sapphire by pulsed laser deposition and characterized by spectroscopic and microscopic techniques. Optical and electrical properties of these films show systematic changes in the band gap and the resistivity with composition. Thus, the optical band gap of the films shows a nearly linear dependence on the composition. The study throws light on the semiconducting nature of the (BN)1–x(C)x thin films with the films exhibiting Efros-Shklovskii (ES) variable range hopping in the low-temperature regime.
Based on a study of the Raman and infrared spectra, normal vibrations of the low-temperature skew-tub (S 4) and high-temperature C i or C2h (skew-chair) forms of P4N4Cl8 have been assigned. A temperature variation study of the Raman spectra has shown the coexistence of both the forms of P4N4Cl8 in the phase transition region. Preliminary assignments of the Raman and infrared spectra of the low- and high-temperature forms of P4N4F8 are presented. One of the low-frequency Raman modes softens through the phase transition of P4N4F8 at 199 K.
