Optical and structural properties of TiO2 films deposited by Sol-Gel technique

TiO2 thin films were prepared by sol gel method. The structural investigations performed by means of X- ray diffraction (XRD) technique, Scanning electronic microscopy (SEM) showed the shape structure at T=600°C. The optical constants of the deposited film were obtained from the analysis of the experimental recorded transmittance spectral data over the wavelengths range 200-3000 nm. The values of some important parameters (refractive index n, dielectric constant ε ∞ and thickness d), and the third order optical nonlinear susceptibility χ(3) of TiO2 film are determined from these spectra. It has been found that the dispersion data obey the single oscillator relation of the Wemple-DiDomenico model, from which the dispersion parameters and high – frequency dielectric constant were determined. The estimation of the corresponding band gap Eg , χ (3) and ε ∞ are 2.57 eV, 0.021 × 10-10 esu and 5.20,respectively.

Preparation, characterization and magnetic studies of Bi0.5X0.5(X=Ca,Sr)MnO3 nanoparticles

Nanoparticles (dia ~ 5 - 7 nm) of Bi0.5X0.5(X=Ca,Sr)MnO3 are prepared by polymer assisted sol-gel method and characterized by various physico-chemical techniques. X-ray diffraction gives evidence for single phasic nature of the materials as well as their structures. Mono dispersed to a large extent, isolated nanoparticles are seen in the transmission electron micrographs. High resolution electron microscopy shows the crystalline nature of the nanoparticles. Superconducting quantum interferometer based magnetic measurements from 10K to 300K show that these nanomanganites retain the charge ordering nature unlike Pr and Nd based nanomanganites. The CO in Bi based manganites is thus found to be very robust consistent with the observation that magnetic field of the order of 130 T are necessary to melt the CO in these compounds. These results are supported by electron magnetic resonance measurements.

Structural, optical, and electrical properties of bulk single crystals of InAsxSb(1-x) grown by rotatory Bridgman method

Radially-homogeneous and single-phase InAsxSb(1−x) crystals, up to 5.0 at. % As concentration, have been grown using the rotatory Bridgman method. Single crystallinity has been confirmed by x-ray and electron diffraction studies. Infrared transmission spectra show a continuous decrease in optical energy gap with the increase of arsenic content in InSb. The measured values of mobility and carrier density at room temperature (for x = .05) are 5.6×104 cm2/V s and 2.04×1016 cm−3, respectively.

Effect of Grain Size on Structural and Magnetic Properties of CuFe2O4 Nanograins Synthesized by Chemical Co-Precipitation

CuFe2O4 nanograins have been prepared by the chemical co-precipitation technique and calcined in the temperature range of 200-1200 degrees C for 3 h. A wide range of grain sizes has been observed in this sintering temperature range, which has been determined to be 4 to 56 nm. Formation of ferrite has also been confirmed by FTIR measurement through the presence of wide band near 600 and 430 cm(-1) for the samples in the as-dried condition. Systematic variation of wave number has been observed with the variation of the calcination temperature. B-H loops exhibit transition from superparamagnetic to ferrimagnetic state above the calcination temperature of 900 degrees C. Coercivity of the samples at lower calcination temperature of 900 degrees C reduces significantly and tends towards zero coercivity, which is suggestive of superparamagnetic transition for the samples sintered below this temperature. Frequency spectrum of the real and imaginary part of complex initial permeability have been measured for the samples calcined at different temperature, which shows wide range of frequency stability. Curie temperature, T-c has been measured from temperature dependence initial permeability at a fixed frequency of 100 kHz. Although there is small variation of T-c with sintering temperature, the reduction of permeability with temperature drastically reduce for lower sintering temperature, which is in conformity with the change of B-H loops with the variation of sintering temperatures.

Enhancing the magnetic characteristics of BiFeO3 nanoparticles by Ca, Ba co-doping

Multiferroic nanoparticles (NPs) of pristine and Ca, Ba co-doped BiFeO3 were synthesized by a facile sal gel route. Co-doping was done by fixing the total dopant concentration at 5 mol% and then the relative concentrations of Ca and Ba was varied. Structural, optical and magnetic properties of the NPs were investigated using different techniques. UV-Vis absorption spectra of BiFeO3 NPs showed a substantial blue shift of similar to 100 nm (530 nm -> 430 nm) on Ca. Ba co-doping which corresponds to increase in band gap by 0.5 eV. Fe-57 Mossbauer spectroscopy confirmed that iron is present only in 3(+) valence state in all co-doped samples. The coercive field increased by 18 times for Bi0.95Ca0.01Ba0.04FeO3 samples, which is the maximum enhancement, observed amongst all the 5 mol% doped samples. At the equimolar (2.5 mol % each) concentration of co-dopants, the coercive field shows a significant enhancement of about 9 times (220 Oe -> 2014 Oe) with concomitant increase in saturation magnetization by 7 times. Thus, equimolar co-doping causes simultaneous enhancement of the twin aspects of magnetic properties thereby making them better suited for device applications. (C) 2012 Elsevier B.V. All rights reserved.

Effect of Oxygen Pressure on Structural and Magnetic Properties of YIG Thin Films

The effect of oxygen pressure (P-O2) on the Yttrium Iron Garnet (YIG) thin films were grown on silicon substrate by rf sputtering method was studied. The as-deposited films at 300K were amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 800 degrees C/1hr in air. The structural, microstructural and magnetic properties were found to be dependent on P-O2.

Phase relationships and magnetic properties of TbxDy1-xFe1.95 alloys

The effect of Tb/Dy ratio on the structural and magnetic properties of (Tb,Dy)Fe-2 class of alloys has been investigated using nine alloys of TbxDy1-xFe1.95 (x = 0-1) covering the entire range. Our results indicate that the three phases viz. (Tb,Dy)Fe-2 (major phase), (Tb,Dy)Fe-3 and(Tb,Dy)-solid solution (minor phases) coexist in all the alloys. The volume fraction of pro-peritectic (Tb,Dy)Fe-3 phase however, has a minimum at x = 0.4 and a maximum at x = 0.6 compositions. The volume fraction of this phase decreases upon heat treatment at 850 degrees C and 1000 degrees C. A Widmanstatten type precipitate of (Tb,Dy)Fe-3 was observed for Dy-rich compositions (0 <= x <= 0.5). The microstructural investigations indicate that the ternary phase equilibria of Tb-Dy-Fe are sensitive to Tb/Dy ratio including the expansion of (Tb,Dy)Fe-2 phase field which is in contrast to the pseudo-binary assumption that is followed in available literature to date. The lattice parameter, Curie temperature and coercivity are found to increase with Tb addition. Split of (440) peak of (Tb,Dy)Fe-2 observed in x >= 0.3 alloys indicate, a spin reorientation transition from 100] to 111] occurs with Tb addition. (C) 2012 Elsevier B. V. All rights reserved.

Benefits of Electronic Wiring and Spacers on Lithium Storage in Nanostructured Lithium-Ion Battery Anodes

The demand for high power density lithium-ion batteries (LIBs) for diverse applications ranging from mobile electronics to electric vehicles have resulted in an upsurge in the development of nanostructured electrode materials worldwide. Graphite has been the anode of choice in commercial LiBs. Due to several detrimental electrochemical and environmental issues, efforts are now on to develop alternative non-carbonaceous anodes which are safe, nontoxic and cost effective and at the same time exhibit high lithium storage capacity and rate capability. Titania (TiO2) and tin (Sn) based systems have gained much attention as alternative anode materials. Nanostructuring of TiO2 and SnO2 have resulted in enhancement of structural stability and electrochemical performances. Additionally, electronic wiring of mesoporous materials using carbon also effectively enhanced electronic conductivity of mesoporous electrode materials. We discuss in this article the beneficial influence of structural spacers and electronic wiring in anatase titania (TiO2) and tin dioxide (SnO2).

Optical and structural properties of nanostructured oxide thin films by sol‐gel technique

TiO2 and Al2O3 are commonly used materials in optical thin films in the visible and near‐infrared wavelength region due to their high transparency and good stability. In this work, TiO2 and Al2O3 single, and nano composite thin films with different compositions were deposited on glass and silicon substrates at room temperature using a sol‐gel spin coater. The optical properties like reflectance, transmittance and refractive index have been studied using Spectrophotometer, and structural properties using X‐Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM).

A unified model for the dynamics of driven ribbon with strain and magnetic order parameters

We develop a unified model to explain the dynamics of driven one dimensional ribbon for materials with strain and magnetic order parameters. We show that the model equations in their most general form explain several results on driven magnetostrictive metallic glass ribbons such as the period doubling route to chaos as a function of a dc magnetic field in the presence of a sinusoidal field, the quasiperiodic route to chaos as a function of the sinusoidal field for a fixed dc field, and induced and suppressed chaos in the presence of an additional low amplitude near resonant sinusoidal field. We also investigate the influence of a low amplitude near resonant field on the period doubling route. The model equations also exhibit symmetry restoring crisis with an exponent close to unity. The model can be adopted to explain certain results on magnetoelastic beam and martensitic ribbon under sinusoidal driving conditions. In the latter case, we find interesting dynamics of a periodic one orbit switching between two equivalent wells as a function of an ac magnetic field that eventually makes a direct transition to chaos under resonant driving condition. The model is also applicable to magnetomartensites and materials with two order parameters. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4790845]

Synthesis, morphology, optical and photocatalytic performance of nanostructured beta-Ga2O3

Fine powders of beta-Ga2O3 nanostructures were prepared via low temperature reflux condensation method by varying the pH value without using any surfactant. The pH value of reaction mixture had great influence on the morphology of final products. High crystalline single phase beta-Ga2O3 nanostructures were obtained by thermal treatment at 900 degrees C which was confirmed by X-ray diffraction and Raman spectroscopy. The morphological analysis revealed rod like nanostructures at lower and higher pH values of 6 and 10, while spindle like structures were obtained at pH = 8. The phase purity and presence of vibrational bands were identified using Fourier transform infrared spectroscopy. The optical absorbance spectrum showed intense absorption features in the UV spectral region. A broad blue emission peak centered at 441 nm due to donor-acceptor gallium-oxygen vacancy pair recombination appeared. The photocatalytic activity toward Rhodamine B under visible light irradiation was higher for nanorods at pH 10.

Effect of TiO2 on electrical and magnetic properties of Ni0.35Cu0.12Zn0.35Fe2O4 synthesized by the microwave-hydrothermal method

The nanocomposites of xTiO(2)+(1-x)Ni0.53Cu0.12Zn0.35Fe2O4 (where 0 <= x >= 1) were prepared using microwave hydrothermal (M H) method at 165 degrees C/45 min. The as-synthesized powders were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The particle size of the powder varies from 18 to 35 nm. The as prepared powders were densified at 500 degrees C/30 min using microwave sintering method. The sintered composites were characterized by XRD and scanning electron microscopy (SEM). The bulk densities of the present composites were increasing with the addition of TiO2. The grain sizes of all the composite vary between 65 nm and 90 nm. The addition of TiO2 to ferrite increased the dielectric properties (epsilon' and epsilon `') also the resonant frequency of all the composites was found to be greater than 1 GHz. The imaginary part of permeability mu `' was found to increase with an increase of TiO2.

Interplay of structural distortions, dielectric effects and magnetic order in multiferroic GdMnO3

Multiferroic materials are characterized by simultaneous magnetic and ferroelectric ordering making them good candidates for magneto-electrical applications. We conducted thermal expansion and magnetostriction measurements in magnetic fields up to 14 T on perovskitic GdMnO3 by highresolution capacitive dilatometry in an effort to determine all longitudinal and transversal components of the magnetostriction tensor. Below the ordering temperature T (N) = 42 K, i.e., within the different complex (incommensurate or complex) antiferromagnetic phases, lattice distortions of up to 100 ppm have been found. Although no change of the lattice symmetry occurs, the measurements reveal strong magneto-structural phenomena, especially in the incommensurate sinusoidal antiferromagnetic phase. A strong anisotropy of the magnetoelastic properties was found, in good agreement with the type and propagation vector of the magnetic structure. We demonstrate that our capacitive dilatometry can detect lattice expansion effects and changes of the dielectric permittivity simultaneously because the sample is housed inside the capacitor. A separation of both effects is possible by shielding the sample. Dielectric transitions could be detected by this method and compared to the critical values of H and T in the magnetic phase diagram. Dielectric changes measured at 1 kHz excitation frequency are detected in GdMnO3 at about 180 K, and between 10 K and 25 K in the canted antiferromagnetic structure which is characterized by a complex magnetic order on both the Gd- and Mn-sites.

The effect of Sb on the electrical and magnetic properties of Ni-Zn ferrites prepared by sol-gel autocombustion method

Polycrystalline Ni-Zn ferrites with a well-defined composition of Ni0.4Zn0.6Fe2-xSbxO4 synthesized using sol-gel method. Morphological characterizations on the prepared samples were performed by high resolution transmission electron and field emission scanning electron microscopy. The powders were densified using microwave sintering method. The room temperature complex permittivity (epsilon' and epsilon aEuro(3)) and permeability (mu' and mu aEuro(3)) were measured over a wide frequency range from 1 MHz-1.8 GHz. The real part of permittivity varies as `x' concentration increases and the resonance frequency was observed at much higher frequencies and there is a significant decrease in the loss factor (tan delta). The electrical resistivity and permeability of NiZn ferrites increased with an increase of Sb content. As the concentration of `x' increases from 0 to 0.08 the saturation magnetisation decreases. The saturation magnetization (M-s) a parts per thousand aEuro parts per thousand 52.211 A.m(2)/Kg for x = 0 at room temperature. The room temperature electro paramagnetic resonance (EPR) were studied.

Physical and magnetic properties of (Co, Ag) doped ZnO nanoparticles

Undoped and (Co, Ag) co-doped ZnO nanostructure powders are synthesized by chemical precipitation method without using any capping agent and annealed in air ambient at 500 A degrees C for 1 h. Here, the Ag concentration is fixed at 5 mol% and Co concentration is increased from 0 to 5 mol%. The X-ray diffraction studies reveal that undoped and doped ZnO powders consist of pure hexagonal structure and nano-sized crystallites. The novel Raman peak at 530 cm(-1) has corroborated with the Co doped ZnO nanoparticles. Moreover, the PL studies reveal that as the Co doping concentration increases and it enters into ZnO lattice as substitutional dopant, it leads to the increase of oxygen vacancies (Vo) and zinc interstitials (Zn-i). From the magnetization measurements, it is noticed that the co-doped ZnO nanostructures exhibit considerably robust ferromagnetism i.e. 4.29 emu g(-1) even at room temperature. These (Co, Ag) co-doped ZnO nanopowders can be used in the fabrication of spintronic and optoelectronic device applications.