- Indian Institute of Science, Materials Research Center, Graduate StudentUniversity of Ulsan, South Korea, Chemical Industry Research Institute, Post-Docadd
- Materials Researcheredit
Here, High Energy Ball Milling (HEBM) is used to prepare Cr doped ZnO (Zn 1-x Cr x O, x = 0-0.04) nanoceramics and their electrical behaviour is studied in detail. The X-ray diffraction suggests a hexagonal wurtzite structure. The... more
Here, High Energy Ball Milling (HEBM) is used to prepare Cr doped ZnO (Zn 1-x Cr x O, x = 0-0.04) nanoceramics and their electrical behaviour is studied in detail. The X-ray diffraction suggests a hexagonal wurtzite structure. The Rietveld refinement XRD pattern of the sample calcined at 900 • C suggests that up to 4 at% of Cr can be doped into the ZnO structure. After sintering, the growth in the particle size was observed for Cr doped ZnO samples. The complex impedance behaviour of samples suggests a decrease in resistance with temperature. This shows the Negative Temperature Coefficient of Resistance (NTCR) characteristic of the Cr doped ZnO sample in the studied temperature range (300-500 • C). At higher temperature, the electrical relaxation behaviour is of the non-Debye type as observed from the relaxation time distribution. The equivalent electrical circuit of ZnO and Cr doped ZnO ceramic samples are a parallel arrangement of bulk capacitance (C b) and bulk resistance (R b).
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In this study, monoclinic LiFeBO 3 was carbon-coated and iodine doped via a solid-state reaction to improve the electrochemical performance of pristine LiFeBO 3 as cathode material in lithium-ion batteries. In order to enhance the... more
In this study, monoclinic LiFeBO 3 was carbon-coated and iodine doped via a solid-state reaction to improve the electrochemical performance of pristine LiFeBO 3 as cathode material in lithium-ion batteries. In order to enhance the electrical conductivity of LiFeBO 3 , the highly electronegative iodide anion was doped in a limited amount (x = 0.005) at the oxygen site of the borate to produce LiFeBO 3Àx I 2x. A thin carbon layer was then deposited in situ on the LiFe-BO 2.995 I 0.01 particles (to produce "LFBI/C") to protect them from air and moisture. Field-emission scanning electron microscopy (FE-SEM) data indicated the aggregated morphology of the synthesized samples. Powder X-ray diffraction (XRD) and 7 Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) measurements revealed that both the doped and undoped LiFeBO 3based samples had mainly monoclinic structures, although a small amount of a vonsenite-type phase was formed upon iodine doping. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) data confirmed the successful insertion of iodine in the cathode material. The specific discharge capacity of LFBI/C at 0.05 C rate (144.68 mAh g À1) was higher than that of carbon-coated LiFeBO 3 (122.46 mAh g À1). The increased capacity of LFBI/C was also evident in long charge-discharge cycles conducted at 1 C rate and in the overall rate performance. Interestingly, the iodine-doped sample exhibited significantly high specific discharge capacity even at 10 C rate.
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Globular amorphous carbonaceous materials embedded with graphite encapsulated metallic Co-nanoparticles with a high degree of crystallinity are synthesized by pyrolysis and demonstrated as excellent candidates for optical limiters.
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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... more
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...
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Phase transformation in cement during hydration is studied by XRD, FTIR and Mössbauer. The hydration process was monitored by self consistent analysis of the XRD results. Alite and belite phases control the early setting time of cement.... more
Phase transformation in cement during hydration is studied by XRD, FTIR and Mössbauer. The hydration process was monitored by self consistent analysis of the XRD results. Alite and belite phases control the early setting time of cement. Mössbauer spectroscopy results suggest that brownmillerite prolongs setting time. a b s t r a c t 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 Mössbauer 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. Mössbauer 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.
The structural, infrared absorption and magnetic property transformations in nanocrystalline Mn 0.5 Zn 0.5 Fe 2 O 4 samples irradiated with different doses (0, 15, 25 and 50 kGy) of γ-irradiation were investigated in this work and a... more
The structural, infrared absorption and magnetic property transformations in nanocrystalline Mn 0.5 Zn 0.5 Fe 2 O 4 samples irradiated with different doses (0, 15, 25 and 50 kGy) of γ-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 γ-radiation. Up to a dose of 25 kGy of γ-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 γ-radiation, the spinel phase decomposed into new stable phases such as α-Fe 2 O 3 and ZnFe 2 O 4 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 γ-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.
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Sm–Gd codoped Mn–Zn ferrite ceramics X-ray diffraction Mössbauer spectroscopy a b s t r a c t We report the evidence of structural changes due to high energy gamma irradiation in Mn 0.4 Zn 0.6 Sm x Gd y Fe 2 À (x þ y) O 4 (where x ¼y... more
Sm–Gd codoped Mn–Zn ferrite ceramics X-ray diffraction Mössbauer spectroscopy a b s t r a c t We report the evidence of structural changes due to high energy gamma irradiation in Mn 0.4 Zn 0.6 Sm x Gd y Fe 2 À (x þ y) O 4 (where x ¼y ¼0.01, 0.02, 0.03, 0.04 and 0.05) ferrites prepared by self-propagating high temperature synthesis method. The structural properties of the as prepared samples and the structural modifications to the samples after gamma irradiation were studied by X-ray diffraction (XRD), Mössbauer spectroscopy and Fourier Transform Infrared (FTIR) Spectroscopy at room temperature. The XRD patterns of the as prepared samples reveal the formation of mixed cubic spinel phase along with small amounts of α-Fe 2 O 3 , SmFeO 3 and/or GdFeO 3 impurity phases. All samples were exposed to gamma radiation dose of 50 kGy originating from a 60 Co source. Our results demonstrate that after gamma irradiation the structure and composition of the various phases in the sample were changed and more stable new phases like ZnFe 2 O 4 , α-Fe 2 O 3 and MnO 2 evolved. As a result the (magnetic) properties of the materials were also altered. Our observation of changes in structural and magnetic properties of the reported ferrites are important for understanding the stability and performance of the materials used in various devices, which are exposed to high energy gamma-rays.