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Synthesis, magnetic and Mossbauer spectroscopic studies of Cr doped lithium ferrite nanoparticles
Srivastava, M.,Layek, S.,Singh, J.,Das, A.K.,Verma, H.C.,Ojha, A.K.,Kim, N.H.,Lee, J.H. Elsevier Sequoia 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.591 No.-
Lithium-based ferrites are promising and potential magnetic materials for microwave applications. They possess a spinel (AB<SUB>2</SUB>O<SUB>4</SUB>) type crystal structure, where the distributions of metal cations over the tetrahedral (A) and octahedral (B) voids play a crucial role for exhibiting different physical properties. Among various parameter of synthesis, pH is an important factor that influences the cation distribution over A and B voids, overall growth of the nanoparticles and different physical properties. In the present work single phase Cr substituted lithium ferrite nanoparticles have been synthesized by the sol-gel method at different pH. The phase identification and crystallite size have been probed by X-ray diffraction studies. The crystallite size changes by 44.2-48.8nm upon varying the pH from 3.5 to 11.5. In order to investigate the cations distribution at A/B sites, Mossbauer spectroscopic measurements were done. The values of magnetic hyperfine field obtained from the Mossbauer data for the A and B sites are ~49.5T and 51T, respectively. Moreover, it is observed that the area ratio of B site to A site increases with increasing the pH. This observation further suggests that the B site is more preferable for Fe<SUP>3+</SUP> cations at higher pH than the A site. The magnetic parameter such as saturation magnetization (M<SUB>s</SUB>), remanent magnetization (M<SUB>r</SUB>), coercive field (H<SUB>C</SUB>) and squareness (S) are determined by vibrating sample magnetometer (VSM) measurements, which show a consistent increase with increasing pH. The reason for the variation in magnetic properties has been explained on the basis of increased Fe<SUP>3+</SUP> cation occupancies at the B site and size effect, which is well supported by Mossbauer spectroscopic and XRD studies.
Singh, Jitendra Pal,Kaur, Baljeet,Sharma, Aditya,Kim, So Hee,Gautam, Sanjeev,Srivastava, Ramesh Chandra,Goyal, Navdeep,Lim, Weol Cheol,Lin, H.-J.,Chen, J. M.,Asokan, K.,Kanjilal, D.,Won, Sung Ok,Lee, The Royal Society of Chemistry 2018 Physical Chemistry Chemical Physics Vol.20 No.17
<P>The interactions of energetic ions with multi-cation compounds and their consequences in terms of changes in the local electronic structure, which may facilitate intriguing hybridization between O 2p and metal d orbitals and magnetic ordering, are the subject of debate and require a deep understanding of energy transfer processes and magnetic exchange mechanisms. In this study, nanocrystals of ZnFe2O4 were exposed to O<SUP>7+</SUP> ions with an energy of 100 MeV to understand, qualitatively and quantitatively, the metal-ligand field interactions, cation migration and magnetic exchange interactions by employing X-ray absorption fine structure measurements and X-ray magnetic circular dichroism to get deeper mechanistic insights. Nanosized zinc ferrite nanoparticles (NPs) with a size of ∼16 nm synthesized in the cubic spinel phase exhibited deterioration of the crystalline phase when 100 MeV O<SUP>7+</SUP> ions passed through them. However, the size of these NPs remained almost the same. The behaviour of crystal deterioration is associated with the confinement of heat in this interaction. The energy confined inside the nanoparticles promotes cation redistribution as well as the modification of the local electronic structure. Prior to this interaction, almost 42% of Zn<SUP>2+</SUP> ions occupied AO4 tetrahedra; however, this value increased to 63% after the interaction. An inverse effect was observed for metal ion occupancies in BO6 octahedra. The L-edge spectra of Fe and Zn reveal that the spin and valence states of the metal ions were not affected by this interaction. This effect is also supported by K-edge measurements for Fe and Zn. The t2g/eg intensity ratio in the O K-edge spectra decreased after this interaction, which is associated with detachment of Zn<SUP>2+</SUP> ions from the lattice. The extent of hybridization, as estimated from the ratio of the post-edge to the pre-edge region of the O K-edge spectra, decreased after this interaction. The metal-oxygen and metal-metal bond lengths were modified as a result of this interaction, as determined from extended X-ray absorption fine structure measurements. These measurements further support the observation of cation migration from AO4 tetrahedra to AO6 octahedra and <I>vice versa</I>. The Fe L-edge magnetic circular dichroism spectra indicate that Fe<SUP>3+</SUP> ions occupying sites in AO4 tetrahedra and BO6 octahedra exhibited antiferromagnetic-like ordering prior to this interaction. The NPs that interacted with energetic O ions displayed a different kind of magnetic ordering.</P>
Jiyaul Haque,K.R. Ansari,Vandana Srivastava,M.A. Quraishi,I.B. Obot 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.49 No.-
The corrosion inhibition performance of two pyrimidine derivatives namely 5-styryl-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d] pyrimidin-4(1H) one (PP-1) and 5-(2-hydroxyphenyl)-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d]-pyrimidin-4(1H) one (PP-2) on N80 steel corrosion in15% HCl has been studied using gravimetric method, electrochemical impedance spectroscopy (EIS),potentiodynamic polarization, atomic force microscopy (AFM), scanning electron microscopy (SEM), DFT,molecular electrostatic potential and Monte Carlo simulation. The corrosion inhibition efficiencies atoptimum concentration (250 mg/L) are 89.1% (PP-1) and 73.1% (PP-2) respectively at 308 K. The corrosioninhibition efficiency increases with increase in concentration and decreases with temperature. PPsobeyed Langmuir adsorption isotherm. AFM and SEM analyses supported formation of protectivefilm onN80 steel in presence of inhibitors. DFT and Monte Carlo simulation calculations supported experimentalresults.
Functionalized Multilayered Graphene Platform for Urea Sensor
Srivastava, Rajesh K.,Srivastava, Saurabh,Narayanan, Tharangattu N.,Mahlotra, Bansi D.,Vajtai, Robert,Ajayan, Pulickel M.,Srivastava, Anchal American Chemical Society 2012 ACS NANO Vol.6 No.1
<P>Multilayered graphene (MLG) is an interesting material for electrochemical sensing and biosensing because of its very large 2D electrical conductivity and large surface area. We propose a less toxic, reproducible, and easy method for producing functionalized multilayer graphene from multiwalled carbon nanotubes (MWCNTs) in mass scale using only concentrated H<SUB>2</SUB>SO<SUB>4</SUB>/HNO<SUB>3</SUB>. Electron microscopy results show the MLG formation, whereas FTIR and XPS data suggest its carboxylic and hydroxyl-functionalized nature. We utilize this functionalized MLG for the fabrication of a novel amperometric urea biosensor. This biosensor shows linearity of 10–100 mg dL<SUP>–1</SUP>, sensitivity of 5.43 μA mg<SUP>–1</SUP> dL cm<SUP>–2</SUP>, lower detection limit of 3.9 mg dL<SUP>–1</SUP>, and response time of 10 s. Our results suggest that MLG is a promising material for electrochemical biosensing applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-1/nn203210s/production/images/medium/nn-2011-03210s_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn203210s'>ACS Electronic Supporting Info</A></P>
Irradiation induced modifications in morphology and magnetic property of Mn/Si structure
M.K. Srivastava,V. Ganesan,P.C. Srivastava 한국물리학회 2010 Current Applied Physics Vol.10 No.4
Mn films of ~50 nm has been deposited by electron beam evaporation technique on cleaned and etched Si [(1 0 0), 8–10 Ω cm] substrates to realize a Mn/Si interfacial structures. The structures have been irradiated from energetic (~100 MeV) ion beam from Mn side. The irradiated and unirradiated structures have been characterized from atomic force microscopy, X-ray diffractometry, magnetic force microscopy,and vibrating sample magnetometer facilities. It has been found that surface/interfacial granular silicide phases (of MnxSiy) are formed before and after the irradiation with a irradiation induced modifications of surface morphology and magnetic property. The surface/interface roughness has been found to increase on the irradiation from the atomic force microscopy data. The magnetic property on the irradiation shows an interesting and significant feature of an increased coercivity and a ferromagnetic like behavior in the Mn–Si structure. The observed increased coercivity has been related to the increased roughness on the irradiation. The ferromagnetism after the irradiation is a curious phenomenon which seems due to the formation of Mn–C–Si compound from the carbon dissolved in silicon.
M.Pramanik,S.K.Srivastava,B.K.Samantaray,A.K.Bhowmick 한국고분자학회 2003 Macromolecular Research Vol.11 No.5
Ethylene vinyl acetate (EVA)/clay nanocomposites were synthesized by blending a solution of ethylene vinyl acetate copolymer containing 12% vinyl acetate abbreviated as EVA-12 in toluene and dispersion of dodecyl ammonium ion intercalated montmorillonite (12Me-MMT) in N,N-dimethyl acetamide (DMAc). X-ray patterns of sodium montmorillonite (Na+-MMT) and 12Me-MMT exhibited d001 peak at 2θ=7.4o and 2θ=5.6o respectively; that is, the interlayer spacing of MMT increased by about 0.39 nm due to intercalation of dodecyl ammonium ions. The XRD trace of EVA showed no peak in the angular range of 3-10o (2θ). In the XRD patterns of EVA/clay hybrids with clay content up to 6 wt% the basal reflection peak of 12Me-MMT was absent, leading to the formation of delaminated configuration of the composites. When the 12Me-MMT content was 8 wt% in the EVA-12 matrix, the hybrid revealed a peak at about 2θ=5.6o, owing to the aggregation of aluminosilicate layers. Transmission electron microscopic photograph exhibited that an average size of 12-15 nm clay layers were randomly and homogeneously dispersed in the polymer matrix, which led to the formation of nanocomposite with delaminated configuration. The formation of delaminated nanocomposites was manifested through the enhancement of mechanical properties and thermal stability, e.g. tensile strength of an hybrid containing only 2 wt% 12Me-MMT was enhanced by about 36% as compared with neat EVA-12.
Some subclasses of multivalent functions involving a certain linear operator
M. K. Aouf,H. Silverman,H. M. Srivastava 장전수학회 2007 Advanced Studies in Contemporary Mathematics Vol.14 No.2
In this paper, we investigate the various important properties and characteristics of the subclasses Sa,c(λ;p,A,B) and Ta,c(λ;p,A,B) of p-valent functions defined by means of certain linear operators. We first establish an inclusion relation for the class Sa,c(λ;p,A,B). We then derive many results for the modied Hadamard products of functions belonging to the class Ta,c(λ;p,A,B). Finally, several applications involving an integral operator and certain fractional calculus operators are also considered.