A. C. Abhyankar

Influence of Texture Coefficient on Surface Morphology and Sensing Properties of W-Doped Nanocrystalline Tin Oxide Thin Films

For the first time, a new facile approach based on simple and inexpensive chemical spray pyrolysis (CSP) technique is used to deposit Tungsten (W) doped nanocrystalline SnO2 thin films. The textural, optical, structural and sensing properties are investigated by GAXRD, UV spectroscopy, FESEM, AFM, and home-built sensing setup. The gas sensing results indicate that, as compared to pure SnO2, 1 wt % W-doping improves sensitivity along with better response (<2 s) and recovery time (<25 s) toward NO2 gas at operating temperatures of ∼225 °C. The optimal composition of 1 wt % W-doped films exhibit lowest crystallite size of the order of ∼8-10 nm with reduced energy band gap and large roughness values of 3.82 eV and 3.01 nm, respectively. Reduction in texture coefficient along highly dense (110) planes with concomitant increase along loosely packed (200) planes is found to have prominent effect on gas sensing properties of W-doped films.

Enhanced absorption of microwave radiations through flexible polyvinyl alcohol-carbon black/barium hexaferrite composite films

Flexible microwave absorber composite films of carbon black (CB)/barium hexaferrite nano-discs (BaF) in polyvinyl alcohol (PVA) matrix, fabricated by gel casting, exhibit ∼99.5% attenuation of electromagnetic waves in the entire 8–18u2009GHz (X and Ku-band) range. The X-ray diffraction and Raman spectroscopy studies confirm the formation of CB-BaF-PVA composite films. The electromagnetic absorption properties of composite films are found to be enhanced with CB content due to the synergetic effect of multiple dielectric and magnetic losses. The 25u2009wt. % CB grafted PVA-BaF flexible composite films with a thickness of ∼u20092 mm exhibit effective electromagnetic shielding of 23.6u2009dB with a dominant contribution from absorption mechanism (SEA ∼u2009 21u2009dB). The dielectric properties of composite films are further discussed by using the Debye model. The detailed analysis reveals that major contribution to dielectric losses is from dipolar and interfacial polarizations, whereas magnetic losses are predominantly from domain...

Dopant driven tunability of dielectric relaxation in MxCo(1-x)Fe2O4 (M: Zn2+, Mn2+, Ni2+) nano-ferrites

Nano-ferrites with tunable dielectric and magnetic properties are highly desirable in modern electronics industries. This work reports the effect of ferromagnetic (Ni), anti-ferromagnetic (Mn), and non-magnetic (Zn) substitution on cobalt-ferrites dielectric and magnetic properties. The Rietveld analysis of XRD data and the Raman spectroscopic study reveals that all the samples are crystallized in the Fd-3m space group. The T2g Raman mode was observed to split into branches, which is due to the presence of different cations (with different vibrational frequencies) at crystallographic A and B-sites. The magnetization study shows that the MnCoFe2O4 sample has the highest saturation magnetization of 87u2009emu/g, which is attributed to the presence of Mn2+ cations at the B-site with a magnetic moment of 5u2009μB. The dielectric permittivity of these nanoparticles (NPs) obeys the modified Debye model, which is further supported by Cole-Cole plots. The dielectric constant of MnCoFe2O4 ferrite is found to be one order...

Titania sensitized with SPADNS dye for dye sensitized solar cell

Synthesis of anatase TiO2 nanoparticle with diameter about 25xa0nm is carried out by using chemical method and powder of TiO2 nanoparticle is pasted on fluorine doped tin oxide (FTO) coated glass by doctor blade. New organic SPADNS dye (C16H9N2Na3O11S3) is used first time to make the dye-sensitized solar cells (DSSC). Cell were constructed by using SPADNS dye loaded wide band gap anatase TiO2 nanoparticle on FTO coated glass as photo-anode, polyiodide as electrolyte, and platinum coated FTO as counter electrode. SPADNS dye was made from organic reagent which is low cost and easy available in market. Better adsorption of SPADNS dye on anatase TiO2 film is due to porous nature of TiO2. This better adsorption gives more transportation of electron from dye to TiO2 which increase the efficiency of solar cell. Although SPADNS dye is the first experiment with TiO2 nanoparticle for DSSC, it gives photocurrent (short-circuit current density) 1.04xa0mA/cm2, open-circuit voltage 0.59xa0V, with 0.9xa0% efficiency under 10xa0mW/m2 LED.

New insights towards strikingly improved room temperature ethanol sensing properties of p-type Ce-doped SnO 2 sensors

In this article, room temperature ethanol sensing behavior of p-type Ce doped SnO2 nanostructures are investigated successfully. Interestingly, it is examined that the abnormal n to p-type transition behavior is caused by Ce doping in SnO2 lattice. In p-type Ce doped SnO2, Ce ion substituting the Sn is in favor of generating excess holes as oxygen vacancies, which is associated with the improved sensing performance. Although, p-type SnO2 is one of the important materials for practical applications, it is less studied as compared to n-type SnO2. Pure and Ce doped SnO2 nanostructures were successfully synthesized by chemical co-precipitation method. The structure, surface morphology, unpaired electrons (such as free radicals), and chemical composition of obtained nanoparticles were studied by various kinds of characterization techniques. The 9% Ce doped SnO2 sensors exhibit maximum sensor response of ~382 for 400u2009ppm of ethanol exposure with fast response time of ~5 to 25u2009sec respectively. Moreover, it is quite interesting that such enhancement of ethanol sensing is unveiled at room temperature, which plays a key role in the quest for better ethanol sensors. These remarkably improved sensing results are attributed to uniformly distributed nanoparticles, lattice strain, complex defect chemistry and presence of large number of unpaired electrons on the surface.

Correlation between the magnetic-microstructure and microwave mitigation ability of MxCo(1−x)Fe2O4 based ferrite–carbon black/PVA composites

A study of controlling the microwave mitigation properties of ferrite-carbon black/PVA composites by tuning the magnetic microstructure and spin arrangement of the ferrite particles is presented. MxCo(1-x)Fe2O4 (M: Ni2+, Mn2+ & Zn2+) nano-ferrites (NFs) were synthesized by a solvothermal method and these NFs were used to fabricate NF-CB hybrids and flexible NF-CB/PVA composite films. The magnetic force microscopy studies of the NFs reveal a unique single axis oriented domain structure for Zn-NFs and multi-domain magnetic microstructures for Mn-NFs and Ni-NFs. Mössbauer analysis of the NFs reveals highly distorted co-ordination of Fe3+ cations in Zn-NFs, whereas sub-lattice spins are canted in Mn-NFs and Ni-NFs. Despite the distorted magnetic lattice and broken coordination, the largest microwave shielding effectiveness (SE) of 32 dB is observed, over a bandwidth of 8 to 18 GHz, for Zn-NF-CB/PVA with a major contribution from absorption (SEA∼ 25 dB). The dielectric properties and Cole-Cole plots indicate enhanced interfacial polarization in Zn-NF-CB/PVA, which is attributed to the motion of polarons across multiple heterogeneous interfaces. These polarons are thought to be generated by distorted co-ordination of Fe3+, and d-d electron transition between Co2+⇋ Fe3+ cations at the B-site of Zn-NF. Distorted co-ordination of Fe3+ in Zn-NF along with unique single axis oriented magnetic domains play a crucial role in magnetic losses, as μ is almost double in Zn-NF based composites as compared to other composites. Due to their excellent and tunable microwave absorption properties, NF-CB/PVA composites could be employed for next generation stealth applications.

Structural, magnetic and dielectric properties of NiZnFe2O4 nanocrystals

In this paper we report the structural, magnetic and dielectric properties of hydrothermally synthesised NiZnFe2O4 nanocrystals. The Rietveld refinement of XRD data reveals that nanoparticles are crystallized in spinel structure with Fd-3m space group and the lattice parameter is found to be 8.413 (2) Ȧ. The FESEM microstructures reveal that the particles are in the spherical shape with a size lying between 20-25u2005nm. The magnetic data analysis shows that the coercivity of the nanoparticles is almost zero at room temperature and the magnetization value is Ms = 45 emu/g. The dielectric relaxation of the NiZnFe2O4 nanocrystals obeys the modified Debye model which considers the more than one ion contributing to the relaxation. The ac-conductivity of these nanocrystals is governed by the universal dielectric response (UDR) model, where the variable-range hopping of localized polarons is responsible for conduction.

Effect of annealing on cation distribution and magnetic properties of nano sized Mn0.34Co0.66Fe2O4 microwave ferrites

Microwave spinel ferrites are ubiquitous in systems that receive, send, and manipulate electromagnetic signals across very high frequency to quasi-optical frequency bands. This paper elaborates the effects of annealing on structural and magnetic properties of the Mn0.34Co0.66Fe2O4 ferrite nano-particles, synthesised by solvothermal method. The Rietveld refinement of XRD data reveals that nanoparticles are crystallized in spinel structure with Fd-3m space group and on annealing the Mn2+ ions migrates from tetrahedral to octahedral site. The FESEM microstructures reveal that grain size increase from 30u2005nm to 200u2005nm on annealing and morphology of the particles changes from spherical to rhombohedral. The magnetic data analysis shows that on annealing the magnetization improves significantly from Ms = 59.23 emu/g to Ms = 86.80 emu/g. Magnetocrystalline anisotropy and coercivity increased significantly on annealing. The change in magnetic properties on annealing is strongly correlated to redistribution of Mn2+ ...

Effect of Zn2+ migration on microstructural and magnetic properties of nano sized Zn0.34Co0.66Fe2O4 particles

This paper elaborates the effects of cationic disorder on structural, microstructural and magnetic properties of the Zn0.34Co0.66Fe2O4 nano-particles, synthesised by solvothermal method followed by annealing at 1000°C. The Rietveld refinement of XRD data reveals that nanoparticles are crystallized in spinel structure with Fd-3m space group. The refinement process reveals that the lattice parameter decrease from 8.392 A to 8.373 A and Zn2+ ions migrate from octahedral to tetrahedral sites on annealing. Comparison of FESEM microstructures reveals that particle size increase from 30u2005nm to 200u2005nm and morphology of the particles changes from spherical to rhombohedral after subjecting them to annealing at 1000°C. The magnetic data analysis shows that magnetization improves significantly from Ms = 47 emu/g to Ms = 64 emu/g at 300u2005K where as magnetocrystalline anisotropy and coercivity reduces upon annealing. The change in magnetic parameters on annealing is strongly correlated to redistribution of Zn2+ cations o...