Abdullah Dar

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Synthesis and Thermal Degradation behavior of the Complexes of Monoethanolamine with Co ( II ) , Ni ( II ) , Zn ( II ) and Cd ( II ) : A Comparative Study

Introduction After the preparation of Aminoalcohols or ethanolamine’s by Wurtz in 1860, they have... more Introduction After the preparation of Aminoalcohols or ethanolamine’s by Wurtz in 1860, they have been used as ligands for the preparation of complexes with many transition metals. The bifunctional nature of ethanolamine’s enables them to serve a variety of commercial applications such as inhibitors [1], surfactants, gas purification and herbicides [2] , Buffers [3] , catalysts [4], ion exchangers [5], additives in building material [6], electroplating [7]and dyes [8]. Ethanolamine’s consists of Mono, Di and Tri ethanolamines. Among them Monoethanolamine is the strongest base. Monoethanolamine act both as monodentate and bidentate ligands [9]. Homo and hetero bimetallic ethanolamine derivatives of a number of metals have also been reported recently [10-13]. The coordination chemistry of aminoalcohols with metal ions deserves further study because they play important role in nature, for example, in hormones [14-15] and in amino sugars [16-17]. Very interesting but contradictory repor...

Hierarchical Vision-Language Alignment for Video Captioning

MultiMedia Modeling, 2018

We have witnessed promising advances on video captioning in recent years, which is a challenging ... more We have witnessed promising advances on video captioning in recent years, which is a challenging task since it is hard to capture the semantic correspondences between visual content and language descriptions. Different granularities of language components (e.g. words, phrases and sentences), are corresponding to different granularities of visual elements (e.g. objects, visual relations and interested regions). These correspondences can provide multi-level alignments and complementary information for transforming visual content to language descriptions. Therefore, we propose an Attention Guided Hierarchical Alignment (AGHA) approach for video captioning. In the proposed approach, hierarchical vision-language alignments, including object-word, relation-phrase, and region-sentence alignments, are extracted from a well-learned model that suits for multiple tasks related to vision and language, which are then embedded into parallel encoder-decoder streams to provide multi-level semantic guidance and rich complementarities on description generation. Besides, multi-granularity visual features are also exploited to obtain the coarse-to-fine understanding on complex video content, where an attention mechanism is applied to extract comprehensive visual discrimination to enhance video captioning. Experimental results on widely-used dataset MSVD demonstrate that AGHA achieves promising improvement on popular evaluation metrics.

Dielectric and impedance spectroscopic analysis in SNP-d embedded PTh nano rods for energy storage applications

Synthetic Metals, 2020

Abstract The heterogeneity and the formation of interfaces between components of a nanocomposite ... more Abstract The heterogeneity and the formation of interfaces between components of a nanocomposite material are important in enhancing the dielectric properties. Na[Fe(CN)4(C3H4N2)NO] 2H2O (SNP-d, the Imidazole derivative of Sodium Nitroprusside) embedded Polythiophene (PTh) nano rods have been prepared by chemical oxidative polymerization method, which is successfully characterized by FTIR, SEM and TEM measurements. Thermogravimetric analysis revealed enhanced thermal stability of PTh/SNP-d nanomaterial as compared to pure PTh. Apparent colossal dielectric constant (CDC) of around ∼2 × 103 in the higher frequency range (10 MHz) at room temperature has been observed. This is owing to the extrinsic (interfacial effects) in addition to intrinsic (bulk) contributions. Heterogeneity in the material paves way for Maxwell-Wagner interfacial effect which is justified by modulus and impedance spectroscopy. The material behaves a non-ideal layered dielectric consisting of a series combination of parallel RC elements. As the nanomaterial shows CDC, a high capacitive effect can therefore be displayed for energy storage applications.

Electric modulus based relaxation dynamics, ac-conductivity and I–V characteristics in PTh/[Co(EDTA)NH3Cl] H2O nanocomposite prepared by chemical oxidation method

Journal of Materials Science: Materials in Electronics, 2017

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Electromagnetic attributes a dominant factor for the enhanced EMI shielding of PANI/Li0.5Fe2.5−xGdxO4 core shell structured nanomaterial

Arabian Journal of Chemistry, 2016

Electromagnetic attributes a dominant factor for the enhanced EMI shielding of PANI/Li 0.5 Fe 2.5... more

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Surfactant-assisted synthesis of polythiophene/Ni0.5Zn0.5Fe2−xCexO4ferrite composites: study of structural, dielectric and magnetic properties for EMI-shielding applications

Physical Chemistry Chemical Physics, 2017

This work reports the exploitation of nanocrystalline Ni0.5Zn0.5Fe2−xCexO4ferrite for EMI shieldi... more

Synthesis and characterization of Li 0.5 Fe 2.5-x Gd x O 4 ferrite nano-particles as a potential candidate for microwave device applications

Materials & Design, 2016

Abstract The effect of Gd substitution on the microstructure, dielectric, impedance and magnetic ... more Abstract The effect of Gd substitution on the microstructure, dielectric, impedance and magnetic properties of Li0.5Fe2.5-xGdxO4 (0.0 ≤ x ≤ 0.2) ferrite nano-crystals prepared by sol–gel auto-combustion method has been investigated. The X-ray diffraction analysis confirmed the cubic spinel phase formation and broadness of reflection peaks indicates the formation of smaller sized particles. The crystallite size was observed to increase from 25.2 nm to 31.1 nm with increasing Gd substitution. The surface morphology and stoichiometric ratio of the compositional elements were analyzed using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Dielectric and impedance measurements were carried out in the frequency range of 100 Hz–10 MHz. The dielectric properties of the present ferrite system were improved much by the substitution of Gd ions. The low dielectric loss at higher frequencies identifies the potential of these ferrites for high frequency applications. The impedance spectroscopy technique was used to study the effect of grain and grain boundary on the electrical properties. An enhancement in the value of saturation magnetization and Curie temperature has been obtained with Gd concentration, which is useful for technological aspects. The coercivity was also observed to decrease with Gd doping, except for the sample with x = 0.20.

Dielectric and impedance study of polycrystalline Li0.35−0.5Cd0.3Ni Fe2.35−0.5O4 ferrites synthesized via a citrate-gel auto combustion method

Journal of Alloys and Compounds, 2015

Abstract Polycrystalline ferrites having general formula Li0.35−0.5XCd0.3NiXFe2.35−0.5XO4 (0.00 ⩽... more Abstract Polycrystalline ferrites having general formula Li0.35−0.5XCd0.3NiXFe2.35−0.5XO4 (0.00 ⩽ X ⩽ 0.08) were prepared using citrate-gel auto combustion method. Doping of Ni2+ ions in Li0.35Cd0.3Fe2.35O4 ferrite has resulted in grain growth inhibition. This has been attributed to the precipitation of Ni2+ ions in the grain boundary region during sintering process. The dielectric permittivity (e′), ac conductivity (σac) and dielectric loss tangent (tan δ) has been measured at different temperatures in the frequency domain of 100 Hz to 5 MHz. The behaviour of tan δ has been observed to show a relaxation phenomenon at relatively higher temperatures. The value of tan δ was also found to increase with temperature, which is an expected behaviour. For composition with X = 0.02, the value of dielectric permittivity was observed to increase. This is a very important feature for power applications of ferrites. Correlated barrier hopping conduction mechanism has been observed in all the samples. For sample with X = 0.00, the small polaron hopping conduction mechanism was observed first, followed by the correlated barrier hopping mechanism. The values of activation energies (Ea) for conduction process, determined from Arrhenius plots have been discussed as a function of Ni content. Nyquist plots have been utilized to delineate the contribution of the resistances of grain and grain boundary with temperature and composition.

An Inexpensive Route to Synthesize High-Purity CrO2 for EMI Shielding in X-Band Frequencies

ISRN Materials Science, 2012

Rod-shaped high-purity samples of CrO2 have been synthesized by an inexpensive and simplified pro... more Rod-shaped high-purity samples of CrO2 have been synthesized by an inexpensive and simplified procedure. Here, we have prepared pure CrO2 without applying any external pressure or control it during synthesis. The sample prepared exhibited an improvement in saturation magnetization values, 68 emu/g at 300 K, 136 emu/g at 80 K, and uniform grained microstructure. The complex permittivity, permeability, and microwave absorption properties of high-purity CrO2 sample were investigated in the 8.2–12.2 GHz (X-band) microwave frequency range. Microwave measurements have shown the high shielding effectiveness due to absorption (SEA) of 20.3 dB. The high value of SEA suggests that CrO2 can be used as a promising electromagnetic shielding, EMI, material in 8.2–12.2 GHz (X-band) microwave frequency range.

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High Magneto-Crystalline Anisotropic Core–Shell Structured Mn 0.5 Zn 0.5 Fe 2 O 4 /Polyaniline Nanocomposites Prepared by in Situ Emulsion Polymerization

The Journal of Physical Chemistry C, 2012

... Optical Gain Performance in Semiconductor Quantum Dots via Coupled Quantum Shells Eva A. Dias... more

Enhanced microwave absorption properties in polyaniline and nano-ferrite composite in X-band

Synthetic Metals, 2010

Highly conducting polyaniline (PANI) nanocomposite with Mn 0.2 Ni 0.4 Zn 0.4 Fe 2 O 4 ferrite was... more Highly conducting polyaniline (PANI) nanocomposite with Mn 0.2 Ni 0.4 Zn 0.4 Fe 2 O 4 ferrite was prepared by mechanical blending. The present work reports the EMI shielding characteristics of the ferrite-Pani nanocomposite with different thickness. The saturation magnetization (Ms) for pure MnNiZn ferrite (52 emu/g) and composite (41 emu/g) was measured by VSM at room temperature. The crystalline size of MnNiZn ferrite was found in the range of 25-30 nm as analyzed by TEM and XRD. The complex permittivity, permeability and shielding effectiveness of the composite for different thicknesses were measured in the 8-12 GHz (X-band) frequency range. The composite of 2.5 mm thickness has shown high shielding effectiveness (49.2 dB) due to absorption (SE A ). The high value of SE A suggests that this composite can be used as a promising absorbing material for X-band frequency range.

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Study of structure and magnetic properties of Ni-doped ZnO-based DMSs

Materials Science in Semiconductor Processing, 2006

Zn 1Àx Ni x O (x ¼ 0:01, 0.02 and 0.05) powders were prepared by a sol-gel method. We have studie... more Zn 1Àx Ni x O (x ¼ 0:01, 0.02 and 0.05) powders were prepared by a sol-gel method. We have studied the structure and magnetic properties of the samples by using X-ray diffraction (XRD), Raman scattering, superconducting quantum interference device (SQUID) and extended X-ray absorption fine structure (EXAFS). The SQUID results showed that all the samples exhibit ferromagnetism above room temperature. From the XRD spectra of the samples, it was obvious that there had no second phase while the Ni-doped concentration was lower than 5 at%. Raman spectra showed an additional band, which is related to the vibration of Ni dopant. The EXAFS was used for the Ni K-edge to probe the local structures of the Ni dopant in ZnO, which show that Ni dopant was substituted for Zn atoms position up to 5 at% Ni concentration.

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Magnetic properties of nano-crystalline Li0.35Cd0.3Fe2.35O4 ferrite prepared by modified citrate precursor method

Materials Chemistry and Physics, 2010

Single phase nano-crystalline lithium cadmium ferrite Li 0.35 Cd 0.3 Fe 2.35 O 4 is synthesized b... more

Study of dielectric and ac impedance properties of citrate-gel synthesized Li0.35Zn0.3Fe2.35O4 ferrite

Journal of Sol-Gel Science and Technology, 2012

... An effect of frequency, crystallite size and sintering temperature on the dielectric constant... more

Minimizing of power loss in Li–Cd ferrite by nickel substitution for power applications

Journal of Magnetism and Magnetic Materials, 2010

The effect of Ni substitution on the microstructure, dielectric, impedance, magnetic and power lo... more The effect of Ni substitution on the microstructure, dielectric, impedance, magnetic and power loss properties has been investigated on a series of Li 0.35-0.5x Cd 0.3 Ni x Fe 2.35-0.5x O 4 (0.00 r x r 0.08) ferrite prepared by citrate precursor method. Dielectric and impedance measurements have been determined in the frequency range 100 Hz-10 MHz. An enhancement in permittivity was observed with Ni concentration and exhibits the maximum value of $ 7 Â 10 3 for x ¼ 0.02 sample. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of all the samples. Power loss measurements have been carried out in the frequency range 50 kHz-5 MHz at induction condition of B ¼ 10 mT. Power loss has been found to be quite low, less than 100 kW/m 3 up to 500 kHz, with the substitution of Ni in Li 0.35-0.5x Cd 0.3 Ni x Fe 2.35-0.5x O 4 ferrite, which is useful for technological aspects.

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Influence of synthesis approach on structural and magnetic properties of lithium ferrite nanoparticles

Journal of Alloys and Compounds, 2012

Nanocrystalline Li 0.5 Fe 2.5 O 4 ferrite particles were synthesized with an average crystallite ... more Nanocrystalline Li 0.5 Fe 2.5 O 4 ferrite particles were synthesized with an average crystallite size of 12.3 nm and 5.7 nm by chemical coprecipitation and reverse microemulsion technique respectively. Zero-field cooled (ZFC) and field cooled (FC) magnetization measurements at different magnetic fields and magnetic hysteresis loops at different temperatures have been measured. The non-saturation of M-H loops with a very low coercivity and remenance at room temperature confirms the presence of superparamagnetic (SPM) nature and single-domain ferrite particles. The blocking temperature (T B ) has been found to shift towards the lower temperature region with the increase in applied magnetic field. It has been attributed to the reduction of magnetocrystalline anisotropy constant and blocking temperature dereases from 145 K to 110 K with increase in field from 50 Oe to 1000 Oe in the samples synthesized by microemulsion method. At high temperature, microemulsion synthesized nanoparticles show a maximum in magnetization versus temperature plot just below the Curie temperature (T C ) which has been attributed to the cumulative effect of the change in anisotropy with temperature and particle size growth during the measurement.

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Magnetic and Electrical Properties of Ti Substituted Lithium Zinc Ferrites

Integrated Ferroelectrics, 2010

Low dielectric loss of Mg doped Ni–Cu–Zn nano-ferrites for power applications

Applied Surface Science, 2012

Magnesium substituted nickel copper zinc nano-ferrite having the general formulae Ni 0.5-x Cu 0.2... more Magnesium substituted nickel copper zinc nano-ferrite having the general formulae Ni 0.5-x Cu 0.2 Zn 0.3 Mg x Fe 2 O 4 (0.0 ≤ x ≤ 0.4) were prepared at relatively lower temperature (900 • C) by sol-gel technique. Thermal gravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy were used for the characterization of as-synthesized samples. It has been observed that the value of permittivity increases to a maximum value of ∼8 × 10 2 for x = 0.4 sample. A remarkable decrease in power loss and loss tangent has been observed with the increase in Mg concentration. The Cole-Cole diagrams were investigated in which a single semi-circle is obtained for all the samples except for the sample with x = 0.4. The presence of two semi-circles for the sample with x = 0.4 indicates that the conduction is due to the grain and grain boundary, while for the rest of the samples the conduction due to the grain boundary is predominant. An improvement in magnetic properties has also observed in the magnesium substituted nickel copper zinc nano-ferrite. Also coercivity was found to decrease with Mg concentration which is useful for power applications.

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