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With time there is an advancement in technology, one technology that advances from generation to generation is mobile networks. There has been a huge evolution in mobile networks in the last few decades. As the data increases there is a need for a faster and higher bandwidth network to access that data. Fast mobile networks include low latency, more secure, and high-rate data transfer. In the last few decades, there has been a vast improvement. The network started from 1G followed by 2G, 3G, 4G, 5G, and it is still going. In this review paper, an attempt has been made to show the difference and advancement between generations by considering various aspects like speed, access time, data transfer time, data rates, and we are also highlighting the challenges and necessities.

We report the mechanism involved in sol-gel auto-combustion synthesis of Ba–Sr-hexaferrite (Ba1-xSrxFe12O19; x = 0, 0.25, 0.5, 0.75 and 1, BSFO) ceramic powders through the analysis of the phases evolved during annealing of the as-synthesized powders, along with their structure and morphological studies. The XRD patterns of the as-synthesized samples indicate the formation of barium/strontium monoferrite ((Ba/Sr)Fe2O4) and maghemite (γ-Fe2O3) phases along with a minute amount of hematite (α-Fe2O3) phase. Annealing of these samples facilitates formation of BSFO phase through the solid state reaction between BaFe2O4 and γ-Fe2O3 phase. Interestingly, after annealing the samples with x = 0, 0.5 and 1, at 1000 °C for 2 h, we observed that phase pure Ba–Sr hexaferrite structure forms, but for samples with x = 0.25 and 0.75, high amount of hematite (α-Fe2O3) phase is observed, especially for x = 0.75. The reason associated with this could be the large difference between the ionic radii of Ba2+ and Sr2+ ions occupying the oxygen site. Furthermore, our study on annealing dependent phase evolution confirms that, this difference in ionic radii forbids the formation of a single phase Ba–Sr hexaferrite. The growth of clear hexagonal-shaped plate-like particles with varied particle sizes was observed for all the samples. The particle size variation may be due to the influence of the ionic radii difference on the sinterability of the samples. Our study provides a better understanding of synthesis mechanism of Ba–Sr hexaferrite samples.

In this work, we have used a single-step pyrolysis method in synthesizing carbonaceous materials at 800 °C and 1000 °C, using metal (Ni- or Mn-) acetylacetonate and toluene as precursors. We demonstrated that the pyrolysis synthesis temperature (TP) and the choice of organometallic precursors affect the morphology and the microstructure of the carbonaceous materials. Namely, at low temperature (800 °C), the Ni(acac)2 precursor leads to the formation of metallic-Ni catalysts for the growth of carbon nanotubes (CNTs), but at high temperature (1000 °C) this favors the growth of carbon globules (CG). In contrast, the Mn-(acac)2 precursor leads to the formation of MnO-particles, and associated carbon globules at both the temperatures used. The electromagnetic interference (EMI) shielding effectiveness (SE) of the PVDF polymer based composite specimens prepared with the carbonaceous samples having a metallic Ni-core is found to be far superior than that obtained using the specimen with particles of the MnO-core. The observed contrast in SE behavior is shown to originate due to the size and metallic nature of the Ni-nanoparticles and the Ohmic conduction loss in these metallic particles over the loss due to interfacial polarization-based scattering of the insulating MnO nanoparticles present in the PVDF-based composite films. Hence, our study highlights the necessary synthesis parameters, and the importance of graphite coated metallic nanoparticles in designing highly efficient EMI shields.

We report the method of tuning the thermal conductivity through the composition of multiwall carbon nanotube (MWCNT) dispersed ethylene glycol based nanofluids. The structure and properties of the MWCNTs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. A parallel plate thermal conductivity (PPTC) set up was fabricated and used for measurement of thermal conductivity of the nanofluids. We have prepared ethylene glycol based nanofluids containing 0.05, 0.1, 0.15, 0.20, 0.25 and 0.35 wt% of MWCNTs. The thermal conductivities of these fluids were measured by keeping them between the two (parallel) plates, referred as the hot and the cold plates, of the sample holder in the PPTC apparatus. The lower plate was water-cooled and the upper plate was heated. The temperature of the hot plate was varied between 35 and 80 °C. The thermal conductivity of the fluids was calculated using the one-dimensional heat conduction equation. According to our observation, an efficient heat transfer occurs through the nanofluids with an optimum concentration of 0.20 wt% of CNTs. Our work demonstrates the importance of the composition of the nanofluids and their structural defects in heat transfer.

In this work, EMI shielding behaviors in the X-band frequency have been investigated for flexible polyvinylidene fluoride (PVDF) composites containing globular- and tubular-shaped carbonaceous nanostructures embedded with mono-metallic (Ni) and bi-metallic (FeNi, CoNi, MnNi) alloy nanoparticles. Pyrolysis was carried out at two different temperatures (800 °C and 1000 °C) to synthesize carbonaceous materials with two different morphologies. Carbon nanotubes (CNTs) are predominantly seen in the samples synthesized at lower temperature (800 °C), whereas carbon globules (CGs) are observed for the samples synthesized at higher temperature (1000 °C). The PVDF-CNT composites show superior microwave shielding behavior than the PVDF-CG composites, which is attributed to the enhanced absorption of the microwave through Ohmic conduction and interfacial polarization loss. The 1-D structure of CNTs provides the required conduction path for the electrons and forms a network to trap the microwave within them via multiple scattering. The microwave absorption behavior of the composites predominantly results from the metallic nature of the embedded nanoparticles, the graphitic layer encapsulating them and the graphitic walls of the CNTs. We further demonstrate the direct correlation of the EMI shielding behavior of the nanocomposites with the morphology of carbonaceous nanomaterials and the conductivity of the embedded metallic nanoparticles.

Synthesis conditions, cation distribution at tetrahedral and octahedral sites and their stability play very important roles in controlling phase-purity and physicochemical properties of spinel ferrite compounds. In this work, an attempt is made to understand how the progress of phase-formation and the structural and magnetic properties are influenced by the annealing temperature and nature of cations used in the synthesis of quaternary spinel ferrite ceramics. A series of Co0.8-xMn0.2ZnxFe2O4 (x = 0, 0.2, 0.4, 0.6 and 0.8) (CMZF) spinel ferrite samples were synthesized by citric acid assisted sol-gel technique followed by annealing at 400, 600 and 800 °C. To compare the progress of phase formation/stability of the cations, simple (binary) spinel ferrite reference samples, such as CoFe2O4, MnFe2O4 and ZnFe2O4, were also synthesized by the same technique and are calcined at the same conditions. In case of CoFe2O4, all the samples have single phase spinel structure, but a transformation from an inverse spinel-type to nearly normal spinel ferrite-type cation distribution is observed with increasing annealing temperature. The as-prepared MnFe2O4 sample and that annealed at 400 °C show formation of single phase spinel ferrite, while those annealed at 600 and 800 °C decomposes completely into Mn2O3, α-Fe2O3 and amorphous-FeO phases. In contrast, for ZnFe2O4 samples, a transformation from the ZnO and α-Fe2O3 phases (present in the as-prepared and up to 600 °C annealed samples) to pure ZnFe2O4–phase occurs only at/above 800 °C. Interestingly, our results show that the progress of the phase formation behavior of the CMZF samples can be predominantly considered as a combination of the behavior and energetics typically exhibited by the individual (simple) ferrite systems. Overall, our work provides the necessary impetus for achieving the phase purity and required physicochemical properties of complex ferrite systems by choosing the cations suitably, based on their nature and annealing behavior.

A series of Fe-doped ZnO (Zn1-xFexO, x = 0, 0.01, 0.03, 0.05, 0.07 and 0.10) samples were synthesized by solution combustion synthesis method using metal nitrates as oxidizers and glycine as fuel. A spongy network-type microstructure is observed by the SEM micrographs of all the synthesized samples. For Fe concentration lower than 0.05 (x ≤ 0.05), formation of phase-pure wurtzite (hexagonal) structured Zn1-xFexO powder with P63mc space group was confirmed from the X-ray diffraction results. However, for x ≥ 0.07, precipitation of ZnFe2O4 impurity phase was observed. Hence, the solubility limit for Fe in ZnO lattice is about x = 0.05 for the samples synthesized by solution combustion method. Two quadruple doublets observed in the 57Fe-Mossbauer spectra for each of the samples suggest that paramagnetic Fe3+ cations occupy two different lattice sites in the ZnO structure; they are the substitutional sites (1) without distortion of the surrounding structure and (2) with distortion due to the defects present in the surrounding structure. In the DRS spectra, an Urbach-like tail was observed in the band gap region, indicating that Fe-doping in the ZnO lattice modifies the electronic structure and enhances the absorption of visible light. Furthermore, the Kubelka-Munk plots suggest the presence of two different local structures validating the Mossbauer results. We studied the photocatalytic degradation of methylene blue dye using these Fe doped ZnO samples as catalysts and the studies revealed that presence of Fe could lead to the formation of carbonaceous material on the surface of the solution combustion synthesized Zn1-xFexO samples. Overall, our results demonstrate the structural characteristics of Fe in Fe-doped ZnO samples synthesized by solution combustion method.

We report that the microstructure, electrical and magnetic properties of the fillers play a very crucial role in synergistically enhancing absorption dominated electromagnetic interference (EMI) shielding in nanocomposites. We prepared nanocomposites by dispersing of varying microstructure and magnetic properties Barium-Lead hexaferrite (BaxPb1−xFe12O19; x = 0.0, 0.4, 0.8 and 1.0) particles and polyaniline (PANI) (light weight conducting species) a in microwave transparent paraffin wax matrix. The EMI shielding behavior of the nanocomposites was studied in the 8–18 GHz frequency band. The hexaferrite powder samples used in the nanocomposites were synthesized by the sol–gel method followed by calcination at 1000°C. The electron micrographs confirm that the pure Pb-hexaferrite sample (x = 0) contains well defined hexagonal plate-like particles. With increase in Ba-content in the samples, the hexagonal particles transform to smaller spherical particles, and the magnetic properties such as coercivity and saturation magnetization change. These modifications in the morphology and magnetic properties of the samples facilitate high attenuation of microwave radiation in our developed nanocomposites. The conducting species (PANI) reflects the microwave from its surface but absorbs it through conduction-loss (Ohmic absorption), whereas the (non-conducting) magnetic Ba-Pb hexaferrite particles absorb the microwave through ferromagnetic resonance but scatter it from their surface due to impedance mismatch. The scattered waves normally increase the electromagnetic smog outside the specimen. To reduce this EM-smog, the Ba-Pb hexaferrite-PANI-Wax nanocomposites provide a synergy among all the electrical and magnetic properties, which leads to very high attenuation through absorption of the scattered electromagnetic wave. Our work demonstrates that the nanocomposites containing Ba-Pb hexaferrite particles are not only efficient in shielding microwave radiation but also help in controlling the electromagnetic-smog.

The steady-state magneto-mechanical response of a magnetorheological fluid (MRF), prepared by dispersing 40 wt % of magnetically soft, light-weight coral-network-shaped yttrium iron garnet (YIG; Y3Fe5O12) powder in silicone oil (140 cSt) is studied as a function of shear rate, under different applied magnetic fields (B). The results show that the yield strength (tau(Y)) and viscosity (eta) of the MRF increase with B, and are strongly influenced by the physical parameters of the particles such as morphology and saturation magnetization. The low density of the YIG-particles, leading to higher volume fraction for equal mass loading, results in a higher viscosity in the absence of a magnetic field, in comparison to that of conventional metallic Fe-particle-based MRFs. Due to this, there is a relatively smaller increase in tau(Y) and eta when the magnetic field is switched on. The YIG-particles-based MRF has the advantages of high chemical stability, thermo-oxidative resistance and low-cost.

Single phase MFeCrO4 (M = Co/Ni) nanosized samples are prepared by solution combustion method using glycine as fuel. Lattice parameter obtained after Rietveld refinement of the powder x-ray diffraction pattern of CoCrFeO4 and NiCrFeO4 samples are 8.374 and 8.325 A and corresponding crystallite sizes are 40 and 27 nm, respectively. FTIR spectra of both samples show tetrahedral and octahedral metal oxygen bond stretching peaks at 596 and 488 cm−1, indicating spinel phase formation. DC magnetisation study indicates that both samples are ferrimagnetic at room temperature, with CoCrFeO4 having a higher value of saturation magnetisation. Mossbauer spectra indicate the presence of magnetic relaxation in the samples. Also, the strength of interaction with nearest neighbour Fe3+ cations is higher in NiCrFeO4.

The structural and magnetic properties of Al substituted yttrium-iron garnet (Y3AlxFe5-xO12, x = 0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6 and 1.8) ceramic powders synthesized using solution combustion method were investigated. Post combustion, the samples were calcination at 1045 °C for 6 h and subsequently at 1200 °C for 6 h to obtain phase-pure garnets. X-ray diffraction (XRD) results confirm the formation of garnets with Ia 3 ¯ d structure. The occupancy of Y3+ ions in the dodecahedral site and the distribution of Al3+ and Fe3+ ions in the tetrahedral and octahedral sites in the bcc structure of the garnet were confirmed by Rietveld refinement of XRD patterns, Mossbauer spectroscopy and 57Fe internal field NMR spectroscopy. For low Al content, Al3+ ions have preference to occupy tetrahedral (Td) sites than the octahedral (Oh) sites. At higher Al content the distribution of Al tends towards a ratio of 3:2 at the tetrahedral:octahedral site. Increase in Al doping results in the decrease in the lattice parameter due to smaller size of Al3+ as compared to Fe3+ ion. All the studied samples show coral-network-like surface morphology. The saturation magnetization (MS) values decrease from ∼26.94 emu/g to ∼ 0.17 emu/g with increase in Al content from 0.0 to 1.8. Further addition of Al makes the sample paramagnetic at RT. Substitution of non-magnetic Al3+ reduces the saturation magnetization rapidly due to the decrease in the superexchange interaction in the crystal.

Aluminium substituted cobalt-nickel ferrite nanoparticles were synthesized by citrate gel auto-combustion method followed by annealing at 1000 °C for 1 h in air. Scanning electron micrographs of all the samples show crystalline particles of irregular morphology with a small variation in particle sizes (~ 110–160 nm). From the analysis of the X-ray diffraction results we observed that the unit cell parameter decreases linearly with increase in aluminium concentration due to the smaller ionic radius of the Al 3+ ions substituting the other cations such as Co 2+ , Ni 2+ and Fe 3+ ions in the compounds. The room temperature Mossbauer spectra of the samples show Zeeman split sextet patterns corresponding to the tetrahedral (Th) and octahedral (Oh) interstitial iron (Fe 3+ ) cations. The observed magnetic hyperfine field (B hf ) decreases with increase in Al-concentration due to the distribution of diamagnetic Al 3+ in the environment of 57 Fe probe atoms. The saturation magnetization measured by Vibrating Sample Magnetometer (VSM) shows a similar trend like that of B hf . The distributions of the cations obtained from the Rietveld refinement and Mossbauer spectroscopy results indicate an increase in Fe 3+ (Th)/Fe 3+ (Oh) occupancy-ratio on increasing Al 3+ concentration, and Ni 2+ cations prefer the octahedral site, whereas Co 2+ and Al 3+ ions redistribute themselves in tetrahedral and octahedral sites, in the ratio 2:3.

The corrosion resistance behavior of graphene oxide (GO) sheets-coated carbonyl iron (CI) microspheres (GO/p-CI sample) was investigated and compared with that of bare CI particles. The GO coating on the CI particles was achieved by utilizing 4-aminobenzoic acid as grafting agent. The cyclic voltammetry of the electrode containing this GO/p-CI sample in 1 mol/L KCl solution does not show any oxidation-peak in contrast to that of the bare carbonyl iron (CI) containing electrode. The charge transfer resistance of GO/p-CI sample was measured to be higher than that of bare CI. The corrosion-potential shifts towards the positive potential direction confirming higher passivity/less corrosive nature of the GO/p-CI sample. Furthermore, the corrosion-current of GO/p-CI sample was lower than that of the bare CI particles. Our results confirm the passivity and excellent corrosion protection behavior of the GO coating on iron structures.

Phase pure Ni substituted Co-Mg nanoferrite (Co0.5Mg0.5-xNixFe2O4, x=0.1, 0.2, 0.3, 0.4, 0.5) powders were synthesized by sol-gel auto-combustion method. Rietveld refined X-ray diffraction patterns and the FTIR results confirmed the single-phase cubic spinel structure of all the samples. Furthermore, all the samples show porous network type morphology. The magnetic measurement results show an increase in saturation magnetization with increase in concentration of Ni in the Co-Mg nanoferrites. Our results demonstrate that the magnetic properties of the Co-Mg ferrites can be tuned via Ni doping.

The present study is carried out to investigate the contribution of iron in the hematite phase in enhancing the reactivity of red mud. Compressive strength test was performed on the binder synthesized from both unpulverized and pulverized red mud. The results indicated an increase in strength of the pulverized red mud based binder. Test results of Mössbauer Spectroscopy showed transition of metastable ferrihydrite phase to hematite phase when the red mud was processed. An increase in line-width of the Moessbauer sextet and an increase in the area of doublet of pulverized red mud based binder hinted at the increase in Fe3+ ions which could have replaced Al3+ ions in the geopolymer network. Results of Fourier-Transform Infrared Spectroscopy (FTIR) test validated the Mössbauer Spectroscopy results. The participation of Fe3+ ions in geopolymerisation was confirmed from the reduction of hematite peak (wavenumber at 462 cm−1). Keywords: Red mud, Pulverization, FTIR, Mössbauer spectroscopy, Compressive strength

The annealing temperature (Ta) dependent development in phase purity, morphology and magnetic properties of BaxPb1-xFe12O19 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) powders synthesized via sol-gel auto-combustion route were studied. The hexagonal phase of PbFe12O19 forms directly via solid-state-reaction between α-Fe2O3 and PbO during annealing of the combustion product at Ta ~ 900 °C, but the BaFe12O19 phase forms at Ta ~ 1200 °C through the formation of BaFe2O4 and α-Fe2O3 as intermediate-phases at low Ta. The BaxPb1-x Fe12O19-phase purity of the samples depend on Ta. For Ta > 1000 °C, PbO evaporates from Pb-containing samples. With increasing Ta, growth of hexagonal-shaped sharp-edged particles was observed for Barium-rich samples, however, the sharp-edges dissolute for Lead-rich samples. High saturation magnetization was observed for Ba-rich samples annealed at 1100 °C. For all the studied samples, magnetic coercivity increases with x but decreases with Ta. The magnetic properties were correlated with the structure, microstructure and grain-size of the samples.

Fuel to oxidizer ratio is a critical parameter that determines the properties of nanocrystalline ferrites prepared by solution combustion method. In this study, the influence of fuel to oxidizer ratio on the purity of phase and physical properties of Zinc and Magnesium ferrite nanoparticles prepared by solution combustion method using glycine as fuel is reported. PXRD and FTIR studies on the samples prepared under fuel lean and fuel rich conditions show that there is a gradual variation in the impurity phase as the F/O ratio is varied. Magnetic studies using VSM and Mossbauer spectroscopy show that a reducing environment is created during the combustion process, which influences the magnetic properties of the samples. Mossbauer studies also show that cation redistribution between the tetrahedral and octahedral sites of the as prepared samples also is an important factor which determines the magnetic properties.

We report the physicochemical insight into the role of coral-shaped yttrium-iron-garnet (YIG) particles for high electromagnetic interference (EMI) shielding behaviour of YIG-polyaniline (PANI)-Wax composites. We studied the total shielding effectiveness (SET) of various compositions of the composites in X and K-u-band frequencies (8-18 GHz) and came upon with a critical concentration (20 wt% of YIG) for which SET is maximum (-44.8 dB). At this critical concentration, the coral shape of YIG helps in effectively increasing the YIG-PANI interfaces necessary for the multiple scattering of electromagnetic (EM) waves. The scattered microwave is then trapped within the dense coral-network of YIG until they are absorbed therein by PANI via conduction loss; thereby, dramatically enhancing the microwave attenuation. The detailed EMI shielding mechanism is explained based on electrical and magnetic properties of the composites. Our result demonstrates the importance of morphology of the dielectric/magnetic particles and their concentration in the composites for designing an efficient EMI shield.

Aluminium substituted yttrium-iron garnet (Y 3 Al x Fe 5-x O 12 , x = 0, 1, 2, 3, 4 and 5) powders were synthesized by the solution combustion route followed by calcination at 1000 °C for 6 h. According to the X-ray diffraction (XRD) results, the as-prepared samples were amorphous. Calcination of the samples at 1000 °C for 6 h results in the formation of phase pure ( Ia 3 d ) garnet structure. The morphology of the samples (for all compositions) were found to be coral-network-like. The Rietveld refinement of the XRD patterns and the Mossbauer spectroscopy confirmed that Y 3+ ions occupy the dodecahedral site, whereas Al 3+ and Fe 3+ ions are distributed in the tetrahedral and octahedral sites of the bcc ( Ia 3 d ) structure of the garnet phase. The Al 3+ ions have a preference to occupy the octahedral site. The lattice parameter decreases with increase in Al 3+ content due to the small size of the Al 3+ cations. For the yttrium-iron-garnet (YIG) sample (x = 0), a saturation magnetization (M S ) value of ~ 29 emu/g was obtained, which decreases to ~ 7 emu/g for the sample with x = 2. Further addition of Al makes the garnets paramagnetic. The coral network shape of our garnet samples renders them useful for various applications in catalysis.

Different shapes of Co-aggregates were synthesized via reduction of a Co salt (CoCl2·6H2O) by chemical precipitation using glycerol, ethylene glycol and ethanol as solvents. The effect of solvent on the morphology, fcc or hcp phase-content and the magnetic properties of the synthesized samples were investigated. The Co-aggregates synthesized using glycerol have a dense spherical shape and high saturation magnetization (MS), whereas ethylene glycol leads to formation of flower-shaped spherical aggregates through loose packing of smaller plate-like particles which have a moderate MS value. When ethanol was used as a solvent, a dendritic (leaf like)-shape of the aggregates with the lowest MS value was obtained. The formation of the obtained morphology of the aggregates was explained based on the size of the solvent molecule, the viscosity of the solvent and the number of polar groups (–OH) present in the solvent molecules. The magnetic domain state and domain wall dynamics of all the Co-samples were investigated using 59Co Internal Field Nuclear Magnetic Resonance (IFNMR) spectroscopy at RT and at 77 K. Through the IFNMR spectroscopy, the presence of gain boundaries, single domain particles and multi-domain particles/aggregates with domain walls associated with fcc and hcp phases were identified and quantified. We observed that the use of ethanol facilitates formation of a higher amount of hcp phase in the sample than the use of glycerol or ethylene glycol.

We synthesized A-site Mn-doped Bi0·5Na0·5TiO3 polycrystalline ceramic ((Bi0·5Na0.5)0.9Mn0·1TiO3 ceramic (BNMT10)) via solid-state reaction route and investigated the structural and temperature-dependent dielectric properties. The dielectric properties of the synthesized samples are explained using the brick-layer model. The relaxation time and corresponding activation energies were obtained through the Arrhenius mechanism by using the imaginary impedance and modulus results. Analysis of the activation energy and other dielectric results suggests that the electric conduction in our BNMT10 sample is due to single and doubly charged oxygen ion vacancy-defects at low and high temperatures, respectively. The grains and grain boundaries contribute to the inherent defect-based conduction mechanism and the dielectric behavior. The electric modulus spectroscopy results discerned the non-Debye type relaxation processes that these processes consist of the localized and long-range relaxation processes. Our results demonstrate that the dielectric behavior of Bi0·5Na0·5TiO3 ceramics can be enhanced through Mn-doping at the A-site.

The effect of reaction temperature, heating rate of the precursors and length of the reaction zone of the furnace on the morphology of carbon nanostructures synthesized via a single-step pyrolysis route is studied. When the furnace was heated at a slow heating rate the synthesized products have highly amorphous globular morphology regardless of the length of the heating zone and the reaction temperature. The amorphous globules contain a dispersion of Fe-based particles. Higher graphitization around the Fe-based particles is observed upon increasing the synthesis temperature. The heating rate has the highest influence on the morphology of the products. When the furnaces were heated (naturally) at a low rate of ∼ 3 °C/min up to the reaction temperature amorphous carbon globules formed, while carbon nanotubes formed when the heating rate was increased to 20 °C/min in a controlled manner. When the synthesized samples were calcined in air at 400 °C for 1 h, the amorphous carbon graphitizes and the graphitic phase forms agglomerated nanotube-like structure.

We report the high energy γ-irradiation induced structural transformations in nanocrystalline Mn 1-x Zn x Fe 2 O 4 (x = 0, 0.25, 0.5, 0.75 and 1) samples synthesized by solution combustion method using a mixture of fuels. All samples were exposed to a gamma radiation dose of 50 kGy. The γ-irradiation decomposes the single phase cubic spinel ( Fd-3m ) structure of the samples into new stable phases. The pure MnFe 2 O 4 sample transformed to Mn 2 O 3 and Fe 1-x O phases whereas the pure ZnFe 2 O 4 sample retained its phase. For the samples with intermediate Zn-content γ-irradiation facilitates the formation of stable α-Fe 2 O 3 and ZnFe 2 O 4 phases, along with amorphous MnO phase. The scanning electron micrographs demonstrate the complete change of the sample morphology with fusion of the particles after γ-irradiation. Our results are important for the understanding of the stability and performance of the devices used in various technological applications near intense high energy radiation sources.

Manganese ferrite (MnFe2O4) nanoparticles were synthesized by sol-gel auto-combustion method using manganese nitrate and ferric nitrate as precursors and citric acid as a fuel. Scanning electron micrographs show irregularly shaped morphology of the particles. The as-prepared samples were annealed at 400, 500, 600 and 800 degrees C for 2 h in air. The phase identification and structural characterizations were performed using powder X-ray diffraction technique along with Mossbauer spectroscopy. Magnetization loops and Fe-57 Mossbauer spectra were measured at RT. After annealing the sample at or below similar to 500 degrees C, we observed two different spinel phases corresponding to two different lattice parameters. This is originating due to the partial oxidation of Mn2+ to Mn3+. At high annealing temperatures (similar to 600 degrees C or above) the spinel MnFe2O4 phase decomposes into crystalline alpha-Mn2O3 and alpha-Fe2O3 phases, and amorphous FeO phase. (c) 2017 Elsevier B.V. All rights reserved.

The structural, infrared absorption and magnetic property transformations in nanocrystalline Mn0.5Zn0.5Fe2O4 samples irradiated with different doses (0, 15, 25 and 50 kGy) of gamma-irradiation were investigated in this work and a mechanism of phase transformation/decomposition is provided based on the metastable nature of the Mn-atoms in the spinel lattice. The nano-powder sample was prepared by solution combustion route and the pellets of the sample were exposed to gamma-radiation. Up to a dose of 25 kGy of gamma-radiation, the sample retained the single phase cubic spinel (Fd-3m) structure, but the disorder in the sample increased. On irradiating the sample with 50 kGy gamma-radiation, the spinel phase decomposed into new stable phases such as alpha-Fe2O3 and ZnFe2O4 phases along with amorphous MnO phase, leading to a change in the surface morphology of the sample. Along with the structural transformations the magnetic properties deteriorated due to breakage of the ferrimagnetic order with higher doses of gamma-irradiation. Our results are important for the understanding of the stability, durability and performance of the Mn-Zn ferrite based devices used in space applications.

We demonstrate the necessity of synergetic absorption and reflection in hard magnetic nanomaterial with conducting polymer for microwave absorption. We investigated various nanocomposites with varied concentrations of phase pure barium hexaferrite (BFO) and polyaniline (PANI) in wax matrix. We found a critical concentration of BFO (Wax: PANI: BFO::50:42:08 wt%, i.e., BFO composition below its percolation threshold) where the Ohmic, dielectric and magnetic losses for the nanocomposites were maximum giving a peak microwave attenuation of 99.85%, out of which 85% attenuation was due to absorption. Beyond this concentration, on either side, the shielding effectiveness decreased. An extraordinary synergy between absorption and reflection was observed when the thickness of the specimen was increased from 1 mm to just 3 mm. The underlying mechanism of synergy was explained via a structural model based on the complex permittivity and permeability values. Our model suggests the necessity of a critical concentration of magnetic materials in a conducting phase for enhancing the microwave absorption.

Using composites of polyvinylidene fluoride (PVDF) and carbon nanostructures embedded with Co-nanoparticles we demonstrate that electromagnetic shielding effectiveness depends strongly on the graphitic carbon concentration and the magnetic properties of Co-particles. Cobalt nanoparticles encapsulated by graphitic carbon embedded in an amorphous carbon-matrix were synthesized by a one-pot pyrolysis method at two different synthesis temperatures, TS = 800 °C (Co-800) and 1000 °C (Co-1000). We demonstrate that TS plays an important role in determining the structure, morphology and magnetic properties of the carbonaceous matrix, the graphite layer and the Co nanoparticles. Higher amounts of graphitic carbon and high saturation magnetization were observed for the Co-1000 sample than that for the Co-800 sample. We observed that the electromagnetic interference (EMI) shielding behavior of the PVDF-Co-1000 nanocomposite shows higher shielding effectiveness than that of the PVDF-Co-800 specimen. A more inhomogeneous dielectric medium in the PVDF-Co-1000 composite results in higher dielectric loss and impedance mismatch. A direct correlation between the shielding effectiveness with dielectric permittivity and magnetic permeability is demonstrated. The synergy between the multiple reflections at the interfaces and absorption of the microwave radiation in the conducting species confirms that a higher degree of graphitization and highly magnetic particles in nanocomposites are effectively superior for EMI shielding of microwave radiation.

The role of improved graphitization-induced conductivity on imparting better electromagnetic interference (EMI) shielding effectiveness (SE) in the X-band frequency regime is demonstrated in pyrolysis-derived Fe3C@C based nanocomposites with PVDF polymer. Variation of synthesis temperature (Ts) is used as a strategic tool to modulate the graphitization and the associated conductivity of Fe3C@C particles. Two different carbonaceous-nanomaterials, both embedded with graphite encapsulated Fe3C-nanoparticles were synthesized at Ts = 800 °C (Fe-800) and Ts = 1000 °C (Fe-1000). We have shown that a higher synthesis temperature results in a thicker well-graphitized carbon-shell around the core (Fe3C) nanoparticles. The better degree of graphitization makes the samples better conducting. These two samples were dispersed separately in flexible polyvinylidene fluoride (PVDF) matrix to form polymer-nanocomposites. The SE of the PVDF:Fe-1000 nanocomposite film is higher than that of the PVDF:Fe-800 nanocomposite film. This high SE of the PVDF:Fe-1000 nanocomposite film is associated with the higher conductivity resulting from the higher degree of graphitization of the Fe-1000 sample. Effectively, the synergetic effects of electric and magnetic losses enhance the absorption-dominated EMI shielding of our nanocomposite-system, making them potential candidates for their direct industrial applications. Simultaneously, our work provides a strategy to control the EMI-SE of nanocomposites through control of the synthesis parameters.

We report the phase transformations in Portland cement before and after hydration. The hydration mechanism was studied in detail by using a full Rietveld refinement of the X-ray diffraction (XRD) patterns, Fourier Transformed Infra-Red (FTIR) spectroscopy, Thermogravimetric Analysis (TGA) and Mossbauer spectroscopy at room temperature. From the Rietveld refinement of XRD data, alite, belite, celite, brown-millerite and low quartz phases were detected and quantified as major phases in dry cement powder. After hydration, calcium carbonate, portlandite and ettringite phases were found to form. A large reduction in the amounts of alite and belite phases were observed suggesting the formation of amorphous C-S-H phase and emphasizing the role of alite phase in flash setting of cement, as justified by the XRD and FTIR spectroscopy. Mossbauer spectra of all the unset samples showed quadrupole split doublets corresponding to the brownmillerite phase which remains unchanged even after about one week of hydration, suggesting that brownmillerite did not transform to other phases during initial stage of hydration process. (C) 2015 Elsevier Ltd. All rights reserved.

The effect of variation of band gap and electronic defect energy levels within the band gap on non-linear optical absorption of 532 nm (green) laser light by coral-like yttrium aluminium-iron garnet (YAIG, Y3Al5-xFexO12) ceramics prepared by solution combustion route is investigated using Z-scan technique. Our yttrium aluminium garnet (YAG) sample with band gap of ≥ ~ 6.5 eV, is transparent to visible light. The band gap of YAG was tuned by substituting Fe at the aluminium site and consequently, the surface defects in YAG were also modified. The defects in the YAIG samples introduce electronic defect states within the band gap. We observed that the intensity of the non-linear absorption (NLA) signal increases with increase in the amount of iron content. We assigned this enhancement of NLA signal to: (1) the decrease in the band gap from ≥ ~ 6.5 eV for YAG to ~ 2.6 eV for yttrium iron garnet (YIG) facilitating two photon absorption (2 PA) process rather than three photon absorption (3 PA), and (2) the increase in excited state absorption (ESA) due to the spread of the defect energy states into the band gap region. As the band gap gets closer to the photon energy of the laser, the non-linear optical absorption is enhanced due to ESA, in combination with the occurrence of the relatively stronger 2 PA process rather than the very weak 3 PA process. Our results demonstrate a method to tune the NLA performance of YAG through iron substitution at the Al sites and provide a better understanding of the non-linear absorption behaviour of YAIG ceramics for their application in optical limiting devices such as laser shields.

The changes in structure, infrared absorption and magnetic property of nanocrystalline Mn0.5Zn0.5SmxFe2-xO4 (x = 0.01, 0.03 and 0.05) ceramics were studied after different doses (0, 15 and 25 kGy) of γ-irradiation. The samples were prepared by solution combustion route. We observed that up to the highest studied dose (25 kGy) of γ-irradiation all the samples retain the cubic spinel (Fd-3m) structure as of the pristine samples, however, the lattice parameter decreases. Furthermore, we observed the metastability of Sm (and Mn) atoms at the octahedral sites. By Sm3+ doping the saturation magnetization of the pristine samples decreases, but the magnetic coercivity increases drastically, indicating enhancement of magnetic anisotropy. After γ-irradiation the magnetic anisotropy vanishes completely and the sample behaves super-paramagnetically with a small variation in saturation magnetization. Our results are important to understand the behavior and stability of the magnetic hardness created by Sm3+ doping in soft magnetic Mn–Zn ferrite ceramics.

EMI shielding properties of nanocomposite containing lead hexaferrite (PFO) and polyaniline (PANI), a conducting polymer, was studied in X and K-u band frequencies. The nanocomposite shows enhanced EMI shielding properties than that of the pure PANI. Incorporation of PFO particles in the PANI enhances the total shielding effectiveness (SET) up to -24 dB at 18 GHz. This means that these nanocomposites can shield similar to 99% of the incoming EM radiation. The PFO/PANI shows much higher attenuation constant values over the measured frequency range. By adding the PFO in the PANI we have created more interfaces between Wax-PFO,Wax-PANI, PANI-PFO and PFO-PANI. These enhanced interfaces lead to Maxwell-Wagner polarization which results in a higher dielectric loss than only PANI.

Homogenously dispersed nanoparticles having a magnetic core and graphitic-carbon shells in amorphous carbon globules are prepared using a low-cost pyrolysis technique. Synergetic microwave absorption in carbon globules embedded with nanoscale iron/iron-carbide graphite (FeC) particles via dielectric, magnetic and Ohmic losses is emphasized in this work. The electromagnetic interference (EMI) shielding properties of the FeC nanoparticles dispersed in polyvinylidene fluoride (PVDF) are studied in the 8–18 GHz frequency range and compared with those of PVDF composites containing similar weight fractions of conducting/magnetic phase micro-particles such as carbonyl iron (CI) or electrolytic iron (EI) or a similar amount of amorphous carbon phase such as amorphous carbon (a-C) globules. The PVDF/FeC composite shows a maximum SET value of −23.9 dB at 18 GHz, as compared to the SET for the other composites. The enhanced EMI shielding in the PVDF/FeC composite is attributed to the increased interfaces of the nanoscale particles, which facilitate enhanced Maxwell–Wagner interfacial polarization. The homogenous dispersion of iron and iron-carbide phases in the carbon matrix of the FeC sample enhances the interfacial polarization and multiple internal scattering of the penetrated EM waves, which get synergistically attenuated by the Ohmic, magnetic and dielectric losses. Based on complex permittivity and permeability results we have calculated the Reflection Loss (RL) of the PVDF/FeC composite. The PVDF–FeC composite shows a RL peak of −40.5 dB for a 4.3 mm thick specimen positioned at 5 GHz frequency. The RL peak is explained using the quarter-wave cancellation model. Our work demonstrates that incorporating carbon globules containing nanoscale magnetic and conducting particles in a polymer matrix, provides an effective way to enhance EMI shielding via absorption of the EM wave in a lightweight thin composite coating.

Unlike silver and gold, indium has material properties that enable strong resonances extended up to the ultraviolet. This extended response, combined with low cost, and ease of synthesis process, makes indium a highly promising material for applications. In this work, we have synthesized ligand-protected indium nanoparticles by a metal reduction method. Powder X-ray diffraction and EDX analyses are consistent with the presence of metallic indium in the nanoparticles. Ligand binding was proven by IR spectroscopy and TGA experiments. TEM analyses reveal that the particle size ranges from 6.3 to 4.8 nm. Optical measurements show that the absorption maximum is red shifted as the particle size decreases.