Effect of Al substitution on the magnetic properties of amorphous Fe73.5Cu1Mo3Si13.5-xAlxB9 alloy

We have synthesized FINEMET type amorphous Fe73.5Cu1Mo3Si13.5-xAlxB9 alloy by the single wheel melt spinning technique. The effect of Al substitution on the magnetic properties has been studied using a vibrating sample magnetometer, SQUID and Mossbauer spectroscopy. Magnetization and Curie temperature of the amorphous phase of the alloys were found to decrease with A] concentration. The results are attributed to the dilution effect of At on the magnetic moment of Fe and to the increase in Fe-Fe interaction distance resulting in the weakening of exchange interaction. (C) 2007 Elsevier B.V. All rights reserved.

Synthesis of Diketopyrrolopyrrole Containing Copolymers: A Study of Their Optical and Photovoltaic Properties

The diketopyrrolopyrrole-based copolymers PDPP-BBT and TDPP-BBT were synthesized and used as donor for bulk heterojunction photovoltaic devices. The photophysical properties of these polymers showed absorption in the range 500-600 nm with a maximum peak around 563 nm, while TDPP-BBT showed broadband absorption in the range 620 - 800 nm with a peak around 656 nm. The power conversion efficiencies (PCE) of the polymer solar cells based on these copolymers and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were 0.68% (as cast PDPP-BBT:PCBM), 1.51% (annealed PDPP-BBT:PCBM), 1.57% (as cast TDPPBBT: PCBM), and 2.78% (annealed TDPP-BBT:PCBM), under illumination of AM 1.5 (100 mW/cm2). The higher PCE for TDPP-BBT-based polymer solar cells has been attributed to the low band gap of this copolymer as compared to PDPP-BBT, which increases the numbers of photogenerated excitons and corresponding photocurrent of the device. These results indicate that PDPP-BBT and TDPP-BBT act as excellent electron donors for bulk heterojunction devices.

Synthesis, structure and magnetic behavior of a new three-dimensional Manganese phosphite-oxalate: [C2N2H10][Mn-2(II)(OH2)(2)(HPO3)(2)(C2O4)]

A novel manganese phosphite-oxalate, [C2N2H10][Mn-2(II)(OH2)(2)(HPO3)(2)(C2O4)] has been hydothermally synthesized and its structure determined by single-crystal X-ray diffraction. The structure consists of neutral manganese phosphite layers, [Mn(HPO3)](infinity), formed by MnO6 octahedra and HPO3 units, cross-linked by the oxalate moieties. The organic cations occupy the middle of the 8-membered one dimensional channels. Magnetic studies indicate weak antiferromagnetic interactions between the Mn2+ ions. (C) 2009 Elsevier Inc. All rights reserved.

Synthesis and characterization of Zn1-xMnxS nanocrystalline films prepared on glass substrates

Nanocrystalline Zn1-xMnxS films (x=0.04, 0.08 and 0.12) were deposited on glass substrates at 400 K using a simple resistive thermal evaporation technique. All the deposited films were characterized by chemical, structural, morphological, optical and magnetic properties. Scanning electron microscopy and atomic force microscopy studies showed that all the films investigated were in nanocrystalline form with the grain size lying in the range 10–20 nm. All the films exhibited cubic structure and the lattice parameters increase linearly with composition. The absorption edge shifted from the higher-wavelength region to lower wavelengths with increase in Mn concentration. The magnetization increased sharply with increase of the Mn content up to x=0.08 and then decreased with further increase of the Mn content. Particularly, Zn0.92Mn0.08S concentration samples show a weak ferromagnetic nature, which might be the optimum concentration for optoelectronic and spintronic device applications.

Size-dependent magnetic properties of iron carbide nanoparticles embedded in a carbon matrix

Here we report on the magnetic properties of iron carbide nanoparticles embedded in a carbon matrix. Granular distributions of nanoparticles in an inert matrix, of potential use in various applications, were prepared by pyrolysis of organic precursors using the thermally assisted chemical vapour deposition method. By varying the precursor concentration and preparation temperature, compositions with varying iron concentration and nanoparticle sizes were made. Powder x-ray diffraction, transmission electron microscopy and Mossbauer spectroscopy studies revealed the nanocrystalline iron carbide (Fe3C) presence in the partially graphitized matrix. The dependence of the magnetic properties on the particle size and temperature (10 K < T < 300 K) were studied using superconducting quantum interference device magnetometry. Based on the affect of surrounding carbon spins, the observed magnetic behaviour of the nanoparticle compositions, such as the temperature dependence of magnetization and coercivity, can be explained.

Optical, Field-Emission, and Antimicrobial Properties of ZnO Nanostructured Films Deposited at Room Temperature by Activated Reactive Evaporation

ZnO nanostructures were deposited on flexible polymer sheet and cotton fabrics at room temperature by activated reactive evaporation. Room-temperature photoluminescence spectrum of ZnO nanostructured film exhibited a week intrinsic UV emission and a strong broad yellow-orange visible emission. TEM and HRTEM studies show that the grown nanostructures are crystalline in nature and their growth direction was indentified to be along [002]. ZnO nanostructures grown on the copper-coated flexible polymer sheets exhibited stable field-emissio characteristics with a threshold voltage of 2.74 V/mu m (250 mu A) and a very large field enhancement factor (beta) of 23,213. Cotton fabric coated with ZnO nanostructures show an excellent antimicrobial activity against Staphylococcus aureus bacteria (Gram positive), and similar to 73% reduction in the bacterial population is achieved compared to uncoated fabrics after 4 h in viability. Using a shadow mask technique, we also selectively deposited the nanostructures at room temperature on polymer substrates.

Sol-Gel Synthesis, characterization and optical properties of Tio2 thin films deposited on ITO/Glass substrates

TiO2 thin films have been deposited on glass and indium tin oxide (ITO) coated glass substrates by sol-gel technique. the influence of annealing temperature on the structural , morphological and optical properties has been examined. X-ray diffraction (XRD) results reveal the amorphous nature of the as-deposited film whereas the annealed films are found to be in the crystalline anatase phase. The surface morphology of the films at different annealing temperatures has been examined by atomic force microscopy (AFM). The in situ surface morphology of the as-deposited and annealed TiO2 films has also been examined by optical polaromicrograph (OPM). TiO2 films infatuated different structural and surface features with variation of annealing temperature. The optical studies on these films suggest their possible usage in sun-shielding applications.

Synthesis, structure, transformation studies and catalytic properties of open-framework cadmium thiosulfate compounds

Five new thiosulfate based inorganic-organic hybrid open-framework compounds have been synthesized employing mild reaction conditions. Of the five compounds, [Na-2(H2O)(8)][Cd(C10H8N2)( S2O3)(2)]center dot 2H(2)O, I and [Cd-2(C10H8N2)(2)(HS2O3)(2)(S2O3)(2)][(C10H9N2)(2)(C10H8N2)(2)]center dot 8H(2)O, II have one-dimensional (1D) structures and [Cd(C10H8N2)(H2O)(2)(S2O3)]center dot 2H(2)O, III, [Cd-2(C10H8N2)(3)(S2O3)(2)], IV and [Cd-2(C10H8N2)(2.5)(S2O3)(2)], V have three- dimensional (3D) structures. The 1D structures are somewhat related, formed by the bonding between tetrahedral Cd centers (CdN2S2) and 4,4'-bipyridine (bpy) units. The inter-chain spaces are occupied by the hanging thiosulfate units in both the cases along with Na(H2O)(6) chains in I and free bpy units in II. The three 3D structures have one-dimensional cadmium thiosulfate chains linked by bpy units. Interpenetration has been observed in all the 3D structures. The 3D structures appear to be related and can be derived from fgs net. Transformation studies on the 1D compound, [Na-2(H2O)(8)][Cd(C10H8N2)(S2O3)(2)]center dot 2H(2)O, I, indicated a facile formation of [Cd(C10H8N2)(H2O)(2)(S2O3)]center dot 2H(2)O, III. Prolonged heating of I gave rise to a 3D cadmium sulfate phase, [Cd-2(C10H8N2)(2)(H2O)(3)(SO4)(2)]center dot 2H(2)O, VI. Compound VI has one-dimensional cadmium sulfate chains formed by six-membered rings connected by bpy units to form a 3D structure, which appears to resemble the topological arrangement of III. Transformation studies of III indicates the formation of IV and V, and at a higher temperature a new 3D cadmium sulfate, [Cd(C10H8N2)(SO4)], VII. Compound VII has a 4 x 4 grid cadmium sulfate layers pillared by bpy units. All the compounds were characterized by PXRD, TGA, IR and UV-visible studies. Preliminary studies on the possible use of the 3D compounds (III-VII) in heterogeneous cyanosilylation of imines appear to be promising.

Electronic phase separation in correlated oxides: The phenomenon, its present status and future prospects

Many transition metal oxide materials of high chemical purity are not necessarily monophasic. Thus, single crystals of chemically pure rare earth manganites and cobaltates of the general formula Ln1-xAxMO3 (Ln=rare earth metal, A=alkaline earth metal, M=Mn, Co) exhibit the phenomenon of electronic phase separation wherein phases of different electronic and magnetic properties coexist. Such phase separation, the length scale of which can vary anywhere between a few nanometers to microns, gives distinct signatures in X-ray and neutron diffraction patterns, electrical and magnetic properties, as well as in NMR and other spectroscopies. While the probe one employs to investigate electronic phase separation depends on the length scale, it is noteworthy that direct imaging of the inhomogeneities has been accomplished. Some understanding of this phenomenon has been possible on the basis of some of the theoretical models, but we are far from unraveling the varied aspects of this new phenomenon. Herein, we present the highlights of experimental techniques and theoretical approaches, and comment on the future outlook for this fascinating phenomenon

Magnetic properties of nanostructured ferrimagnetic zinc ferrite

Nanostructured ZnFe2O4 ferrites with different grain sizes were prepared by high energy ball milling for various milling times. Both the average grain size and the root mean square strain were estimated from the x-ray diffraction line broadening. The lattice parameter initially decreases slightly with milling and it increases with further milling. The magnetization is found to increase as the grain size decreases and its large value is attributed to the cation inversion associated with grain size reduction. The Fe-57 Mossbauer spectra were recorded at 300 K and 77 K for the samples with grain sizes of 22 and 11 nm. There is no evidence for the presence of the Fe2+ charge state. At 77 K the Mossbauer spectra consist of a magnetically ordered component along with a doublet due to the superparamagnetic behaviour of small crystalline grains with the superparamagnetic component decreasing with grain size reduction. At 4.2 K the sample with 11 nm grain size displays a magnetically blocked state as revealed by the Mossbauer spectrum. The Mossbauer spectrum of this sample recorded at 10 K in an external magnetic field of 6 T applied parallel to the direction of gamma rays clearly shows ferrimagnetic ordering of the sample. Also, the sample exhibits spin canting with a large canting angle, maybe due to a spin-glass-like surface layer or grain boundary anisotropies in the material.

Synthesis,characterization and photoluminescence properties of CaSiO3 :Dy3+ nanophosphors

CaSiO3 : Dy3+ (1-5 mol. %) nanophosphors were synthesized by a simple low-temperature solution combustion method. Powder X-ray diffraction patterns revealed that the phosphors are crystalline and can be indexed to a monoclinic phase. Scanning electron micrographs exhibited faceted plates and angular crystals of different sizes with a porous nature. Photoluminescence properties of the Dy3+-doped CaSiO3 phosphors were observed and analyzed. Emission peaks at 483, 573 and 610 nm corresponding to Dy3+ were assigned as F-4(9/2)-> H-6(15/2), F-4(9/2) -> H-6(13/2) and F-4(9/2) -> H-6(11/2) transitions, respectively, and dominated by the Dy3+ F-4(9/2) -> H-6(13/2) hyperfine transition. Experimental results revealed that the luminescence intensity was affected by both heat treatment and the concentration of Dy3+ (1-5 mol. %) in the CaSiO3 host. Optimal luminescence conditions were achieved when the concentration of Dy3+ was 2 mol. %. UV-visible absorption features an intense band at 240 nm, which corresponds to an O-Si ligand-to-metal charge transfer band in the SiO32- group. The optical energy band gap for the undoped sample was found to be 5.45 eV, whereas in Dy3+-doped phosphors it varies in the range 5.49-5.65 eV. The optical energy gap widens with increase of Dy3+ ion dopant.

Structural and spectral perspectives of a novel thiosemicarbazone synthesized from di-2-pyridyl ketone and 4-phenyl-3-thiosemicarbazide

A new thiosemicarbazone, HL is synthesized from di-2-pyridyl ketone and 4-phenyl-3-thiosemicarbazide and structurally and spectrochemically characterized. H-1 NMR, C-13 NMR, COSY, HMQC and IR spectra of the compound are studied and the proton magnetic resonance spectrum reveals some unprecedented observations. The thione form is predominant in the solid state, as supported by the crystal structure and IR data, while a thiol-thione equilibrium is proposed in the solution state by NMR studies. The compound crystallizes into a monoclinic lattice with space group C2/c and the ZE conformation is exhibited by the thiosemicarbazone. Intra- and intermolecular hydrogen-bonding interactions give rise to a two-dimensional packing in the crystal lattice

Synthesis, characterization and photoluminescence properties of Gd2O3:Eu3+ nanophosphors prepared by solution combustion method

Gd2O3:Eu3+ (0.5-8.0 mol%) nanophosphors have been prepared by low temperature solution combustion method using metal nitrates as oxidizers and oxalyl dihydrazide (ODH) as a fuel. The phosphors are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and photoluminescence (PL) techniques. PXRD patterns of as-formed and calcined (800 degrees C, 3 h) Gd2O3 powders exhibit monoclinic phase with mean crystallite sizes ranging from 20 to 50 nm. Eu3+ doping changes the structure from monoclinic to mixed phase of monoclinic and cubic. SEM micrographs shows the products are foamy, agglomerated and fluffy in nature due to the large amount of gases liberated during combustion reaction. Upon 254 nm excitation the photoluminescence of the Gd2O3:Eu3+ particles show red emission at 611 nm corresponding to D-5(0)-> F-7(2) transition. It is observed that PL intensity increases with calcination temperature. This might be attributed to better crystallization and eliminates the defects, which serve as centers of non-radiative relaxation for nanomaterials. It is observed that the optical energy gap (E-g) is widened with increase Eu3+ content. (C) 2010 Elsevier B.V. All rights reserved.

A series of transition metal-azido extended complexes with various anionic and neutral co-ligands: synthesis, structure and their distinct magnetic behavior

The crystal structures and magnetic properties of five new transition metal-azido complexes with two anionic [pyrazine-2-carboxylate (pyzc) and p-aminobenzoate (paba)] and two neutral [pyrazine (pyz) and pyridine (py)] coligands are reported All five complexes were synthesized bysolvothermal methods The complex [Co-2(pyzc)(2)(N-3)(2)(H2O)(2)](n) (1) is 1D and exhibit canted antiferromagnetism, while the 3D complex [MnNa(pyzc)(N-3)(2)(H2O)(2)](n) (2) has a complicated structure and is weakly ferromagnetic in nature [Mn-2(paba)(2)(N-3)(2)(H2O)(2)](n) (3). is a 2D sheet and the Mn-II ions are found to be antiferromagnetically coupled The isostructural 2D complexes [Cu-3(pyz)(2)(N-3)(6)](n) (4) and [Cu-3(py)(2)(N-3)(6)](n) (5) resemble remarkably in their magnetic properties exhibiting moderately strong ferromagnetism. Density functional theory calculations (B3LYP functional) have been performed to provide a qualitative theoretical interpietation of the overall magnetic behavior shown by these complexes.

Structural and spectral perspectives of a novel thiosemicarbazone synthesized from di-2-pyridyl ketone and 4-phenyl-3-thiosemicarbazide

A new thiosemicarbazone, HL is synthesized from di-2-pyridyl ketone and 4-phenyl-3-thiosemicarbazide and structurally and spectrochemically characterized. H-1 NMR, C-13 NMR, COSY, HMQC and IR spectra of the compound are studied and the proton magnetic resonance spectrum reveals some unprecedented observations. The thione form is predominant in the solid state, as supported by the crystal structure and IR data, while a thiol-thione equilibrium is proposed in the solution state by NMR studies. The compound crystallizes into a monoclinic lattice with space group C2/c and the ZE conformation is exhibited by the thiosemicarbazone. Intra- and intermolecular hydrogen-bonding interactions give rise to a two-dimensional packing in the crystal lattice. (c) 2005 Elsevier B.V. All rights reserved.