Synthesis and photocatalytic properties of AgLi1/3Ru2/3]O-2: A new delafossite oxide

A new delafossite oxide, AgLi1/3Ru2/3]O-2, synthesized by ion-exchanging interlayer-Li+ with Ag+ in layered Li2RuO3, is reported. The transformation of layered Li2RuO3 (monoclinic, space group C2/c) to AgLi1/3Ru2/3]O-2 possessing a delafossite structure (space group R (3) over barm) has been established with powder X-ray diffraction. The successful conversion of LiLi1/3Ru2/3]O-2 to AgLi1/3Ru2/3]O-2 is further confirmed by EDAX analysis. The diffuse reflectance spectrum of AgLi1/3Ru2/3]O-2 shows broad absorption in the UV-visible region suggesting its use as a photocatalyst. The photocatalytic activity of AgLi1/3Ru2/3]O-2 has been investigated by degrading various dyes. It showed significant photocatalytic activity for dye degradation both under UV and solar radiation. (C) 2010 Elsevier B.V. All rights reserved.

Poly-ols Based Sol-Gel Synthesis of Zinc Oxide Thin Films

We demonstrate that the structural and optical properties of a sol-gel deposited zinc oxide thin film can be tuned by varying the composition of the sol, consisting of ethylene glycol and glycerol. A systematic study of the effect of the composition of sol on the mean grain size, thickness, and defect density of the zinc oxide film is presented. About 20% glycerol content in the sol is observed to improve the quality of the film, as evaluated by X-ray diffraction and photoluminescence studies. Thus, optimizing the composition of the sol for about 60 nm thick ZnO film using 20% glycerol resulted in the zinc oxide film that is about 80% transparent in visible spectrum, exhibiting electrical resistivity of about 18 Omega cm and field-effect mobility of 0.78 cm(2)/(V s). (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3515894] All rights reserved.

Electron paramagnetic resonance studies on Mn doped GaSb

We report on the X-band (similar to 9.43 GHz) electron paramagnetic resonance (EPR) investigations carried out on polycrystalline Ga1-xMnxSb (x=0.02). A strong EPR signal with an effective g factor (g(eff)) close to 2.00 was observed, suggesting that the ionic state of Mn which replaces Ga ion in the lattice, is Mn2+ attributable to Delta M=1 transition of the ionized Mn acceptor A(-), Mn (3d(5)). The apparent absence of EPR signal, typical for neutral Mn acceptor at g=2.7 suggests either no such centers are present or the signal broadens beyond detection limit. The temperature dependent EPR studies combined with dc magnetization data suggest the possible coexistence of antiferromagnetic and ferromagnetic phases at very low temperatures. (C) 2011 American Institute of Physics. doi:10.1063/1.3543983]

Second harmonic generation in poled molecularly doped polymer films : Push-pull butadienes in poly(methyl methacrylate) and polystyrene

We report second harmonic generation in a new class of organic materials, namely donor-acceptor substituted all-trans butadienes doped in poly(methyl methacrylate) or polystyrene and oriented by corona poling at elevated temperatures. Second harmonic measurements were made at room temperature. The observed d33 coefficients are greater than those of potassium dihydrogen phosphate or 4-dimethylamino-4'-nitrostilbene doped in similar polymer matrices. Rotational diffusion coefficients estimated from the decay characteristics of the second harmonic intensity in the polymer films indicate that the polymer matrix plays a major role in stabilizing the dopants in a nonlinear optics conducive environment.

An electron-spin-resonance study of MN2+ doped calcium hydrazine carboxylate monohydrate

Single crystals of calcium hydrazine carboxylate, monohydrate have been studied by ESR of Mn2+ doped in the calcium sites. X-band ESR indicated a large crystal field splitting necessitating experiments at Q band. The analysis shows two magnetically inequivalent (but chemically equivalent) sites with g(xx) = 2.0042+/-0.0038, g(yy) = 2.0076 +/-00029, g(zz) =2.0314+/-0.001, A(zz) = 0.0099+/-0.0002 cm(-1), A(xx) = 0.0099+/-0.0002 cm(-1), A(yy) = 0.0082+/-0.0002cm(-1), D = 3/2D(zz) = 0.0558+/-0.0006cm(-1), and E = 1/2(D-xx-D-yy) = 0.0127+/-0.0002 cm(-1).One of the principal components of the crystal field, (D-zz), is found to be along the Ca<->Ca direction in the structure and a second one, (D-xx), along the perpendicular to the plane of the triangle formed by three neighbouring calciums. The A tensor is found to have an orientation different from that of the g and D tensors reflecting the low symmetry of the Ca2+ sites.

Electrochemical preparation of few layer-graphene nanosheets via reduction of oriented exfoliated graphene oxide thin films in acetamide-urea-ammonium nitrate melt under ambient conditions

Electrochemical reduction of exfoliated graphene oxide, prepared from pre-exfoliated graphite, in acetamide-urea-ammonium nitrate ternary eutectic melt results in few layer-graphene thin films. Negatively charged exfoliated graphene oxide is attached to positively charged cystamine monolyer self-assembled on a gold surface. Electrochemical reduction of the oriented graphene oxide film is carried out in a room temperature, ternary molten electrolyte. The reduced film is characterized by atomic force microscopy (AFM), conductive AFM, Fourier-transform infrared spectroscopy and Raman spectroscopy. Ternary eutectic melt is found to be a suitable medium for the regulated reduction of graphene oxide to reduced graphene oxide-based sheets on conducting surfaces. (C) 2010 Elsevier B.V. All rights reserved.

Creep in TiO2 doped Zirconia: Implications for high strain rate superplasticity

In ceramics, dopants offer the possibility of higher creep rates by enhancing diffusion. The present study examines the potential for high strain rate superplasticity in a TiO2 doped zirconia, by conducting creep experiments together with microstructural characterization. It is shown that both pure and doped zirconia exhibit transitions in creep behaviour from Coble diffusion creep with n similar to 1 to an interface controlled process with n similar to 2. Doping with TiO2 enhances the creep rate by over an order of magnitude. There is evidence of substantial grain boundary sliding, consistent with diffusion creep.

Bi2W1–xCuxO6–x(0.7[less-than-or-eq]x[less-than-or-eq]0.8): a new oxide-ion conductor

Anion-deficient Aurivillius phases of the general formula, Bi2Wi-xCuxO6-2x, possessing orthorhombic/tetragonal Bi2WO6-like structures, have been synthesized by quenching the oxide melts. The tetragonal phase stabilized for the compositions 0.7 less-than-or-equal-to x less-than-or-equal-to 0.8 is a good oxide-ion conductor in the temperature range 500-900 K, the x = 0.7 composition exhibiting the highest conductivity in the series.

Chemical Approaches to the Design of Oxide Materials.

Chemical methods of synthesis play a crucial role in designing and discovering new and novel materials and in providing less cumbersome methods for preparing known materials. Chemical methods also enable the synthesis of metastable materials which are otherwise difficult to prepare. In this presentation, the various innovative chemical methods of synthesising oxide materials will be briefly reviewed with emphasis on soft-chemical routes. Electrochemical synthesis, ion-exchange method, alkali-flux method and some of the interaction reactions will be highlighted, besides topochemical aspects of solid state synthesis. Cuprate superconductors as well as intergrowth structures will also be examined.

Combustion synthesis and properties of Ln3Fe5O12 and yttrium aluminium garnets

The rare earth iron garnets Ln3Fe5O12 and Y3AlxFe5-xO12, where x=1.0-5.0, and Y1.5Gd1.5Al0.2Fe4.8O12 have been prepared by the combustion of redox mixtures containing corresponding metal nitrates and oxalyl dihydrazide, i.e. C2H6N4O2 at 350-degrees-C. The solid combustion products are amorphous, submicrometre-sized powders which, on heating at 750-degrees-C for 3 h, yield crystalline single-phase garnets. The particle size of the garnets is below 1 mum and the surface area ranges from 16 to 90 m2 g-1. Yttrium iron garnet could be sintered to a density of more than 95% at 1200-degrees-C for 3 h, giving an average grain size of 3-5 mum.

Combustion synthesis of oxide materials for nuclear waste immobilization

Oxide materials like perovskite, zirconolite, hollandite, pyrochlore, NASICON and sphene which are used for nuclear waste immobilization have been prepared by a solution combustion process. The process involves the combustion of stoichiometric amount of corresponding metal nitrates and carbohydrazide/tetraformyl trisazine/diformyl hydrazide at 450 degrees C. The combustion products have been characterized using powder X-ray diffraction, infrared spectroscopy, and Si-29 MAS-NMR. The fine particle nature of the combustion derived powders has been studied using density, particle size, BET surface area measurements and scanning electron microscopy. Sintering of combustion derived powder yields 85-95% dense ceramics in the temperature range 1000 degrees-1300 degrees C.

Growth and characterization of laser-deposited Ag-doped YBa2Cu3O7−x thin films on bare sapphire

Microstructural and superconducting properties of YBa2Cu3O7-x thin films grown in situ on bare sapphire by pulsed laser deposition using YBa2Cu3O7-x targets doped with 7 and 10 wt% Ag have been studied. Ag-doped films grown at 730 degrees C on sapphire have shown very significant improvement over the undoped YBa2Cu3O7-x films grown under identical condition. A zero resistance temperature of 90 K and a critical current density of 1.2 x 10(6) A/cm(2) at 77 K have been achieved on bare sapphire for the first time. Improved connectivity among grains and reduced reaction rate between the substrate and the film caused due to Ag in the film are suggested to be responsible for this greatly improved transport properties.

Influence of deviation from stoichiometry on the photoluminescence in CdTe doped with indium

Low temperature photoluminescence of vacuum and cadmium annealed CdTe:In is reported here. A new peak at similar to 1.14 eV related to transitions from the conduction band to an acceptor involving a tellurium vacancy has been observed.

Optical absorption and photoluminescence studies of Nd3 doped alkali boro germanate glasses

Optical absorption and photoluminescence studies have been carried out at room temperature in 25 R2O-25 GeO2-49.5 B2O3-0.5 Nd2O3 glass systems, (Composition in mol%, R= Li, Na, K and Rb). Judd Ofelt Intensity parameters and other parameters like Racah (E-1, E-2 and E-3), Slater-Condon-Shortley (F-2, F-4 and F-6) Spin-Orbit Coupling (xi(4f)) and Configuration Interaction (alpha,beta and gamma) for Nd3+ ion in the glass system are calculated. The variation of the 02 parameters are interpreted in terms of the covalency of the RE ion in the glass matrix. Further the hypersensitive transition I-4(9/2) -> (4)G(5/2), (2)G(7/2) is analyzed with respect to the intensity ratio I-L/I-S and is found to be dependent on the type of alkali in the glass matrix. The Photoluminescence studies do not show any appreciable shift in the peak emission wavelength of the F-4(3/2) to I-4(11/2) transition with the change in alkali type. (C) 2010 Elsevier B.V. All rights reserved.

Influence of grain boundary sliding on diffusion in yttria doped zirconia

Grain boundary sliding during high temperature deformation can lead to stress concentrations and an enhancement of diffusion in mobile boundaries. Experiments were conducted on a fine grained 3 mol% yttria stabilized tetragonal zirconia, under conditions associated with superplastic flow involving grain boundary sliding. Tracer diffusion studies under creep conditions and without load indicate that there is no enhancement in either the lattice or grain boundary diffusivities. The experimental creep data are consistent with an interface controlled diffusion creep mechanism. (C) 2011 Elsevier Ltd. All rights reserved.