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Influence of cooling rate on the magnetic properties of Hf-Co-Fe-B melt-spun alloy
Get PDFIn the present work, Hf2Co9.5Fe1.5B melt-spun (MS) alloy is synthesized by employing melt spinning at different wheel speeds viz. 16, 20, 24 and 28 m/s to study the effect of quenching on the thermal, structural, microstructural and magnetic properties. The phase purity and the magnetic behaviour of the MS ribbons are highly dependent on the cooling rate that is controlled by altering the tangential wheel speed during melt spinning. Cooling rates are found to increase with increase in wheel speed with a concurrent decrease in the ribbon thickness owing to the increase in the heat transfer coefficient at the thermal contact. The best phase purity and the magnetic properties are found for the ribbons melt-spun at 28 m/s. This could be attributed to the high cooling rate 2.3 x 10(7) K/s causing crystallization of hard magnetic Hf2Co11B phase leading to refined grain size. A maximum coercivity (H-C) similar to 2.18 kOe, remanence ratio (M-r/M-s) similar to 0.61, an appreciable magnetic energy product (BH)(max) similar to 3 MGOe observed in the MS ribbons at 28 m/s illustrates the critical role of wheel speed in the enhancement of permanent magnetic properties in a single-step without annealing. XRD patterns reveal that the alloy was found to crystallize in orthorhombic Hf2Co11B in addition to cubic Co and Hf6Co23 phases. FE-SEM analysis is carried out to realize the grain morphology and phase identification. The current work exhibits the efficacy of rapid quenching by melt spinning as an effective technique in the development of high-performance Hf2Co9.5Fe1.5B rare-earth-free permanent magnet alloy for future energy applications in the high-temperature regime
Journey of Kilogram from Physical Constant to Universal Physical Constant (h) via Artefact: A Brief Review
Get PDFThe redefinition of mass adopted in November 2018 and implemented from 20 May 2019, i.e. World Metrology Day, eliminated the artefact-based approach dependent upon the International Prototype of the Kilogram (IPK), in favour of realizing the kilogram in terms of the Planck constanthby fixing its value as 6.62607015 x 10(-34) J s. In this paper, the authors present a general outline of the circumstances and related developments that paved the way for the new definition that replaced the IPK after a period of 130 years since it was formally sanctioned to define the kilogram in 1889. The new definition opens up fascinating developments in mass metrology which include different realization techniques, realizing the unit at values other than 1 kg, numerous sources for traceability can be envisaged etc
Magnetic phase profile in La0.7Ca0.3MnO3/Pr0.58Ca0.42MnO3 superlattices: Role of substrate inherent disorders
No full textWe report the impact of dissimilar substrate inherent twinning over the structural, electrical and magnetic properties of otherwise identical ferromagnetic/antiferromagnetic La0.7Ca0.3MnO3/Pr0.58Ca0.42MnO3 (LCMO/PCMO) superlattices (SLs). 12 layers of LCMO and PCMO each similar to 11 nm thick were deposited and then LCMO was deposited as the top layer. The SLs were fabricated by RF magnetron sputtering method over three LaAlO3 (0 0 1) substrates embodied with different twinning disorders. Structural analysis employing high resolution X-ray diffraction (HRXRD; 2 theta, omega, and phi scans) demonstrates that substrate twin structures exactly get imprinted over all the superlattice peaks. Transport and magnetization measurements showed coupled insulator-metal (IM)/paramagnetic-ferromagnetic (PM-FM) transition around 220 K in all the three SLs. In the high temperature PM region all the samples behave similarly however at low temperatures where long-range ferromagnetic metal (FMM) and antiferromagnetic insulating (AFMI) phases start emerging in LCMO and PCMO respectively, SLs show deviant behaviors. This is ascribed to the substrate originated microstructural disorders in SLs which are distinct for all the samples and hence perturb FMM/AFMI interfacial interactions differently. Samples with prominently large substrate FWHM = 0.683 degrees and 0.959 degrees respectively show a second but weak IM transition and a strong hysteretic IM transition behavior. Magnetization displays a hysteretic behavior in field cooled data measured during cooling and warming cycles. The hysteresis gets stronger with the rise in FWHM which signifies an enhancement of phase competition between FMM and AFMI phases at the interfaces. This behavior of LCMO/PCMO SLs is attributed to the interfacial exchange interactions lead magnetic reconstruction at the interfaces
Influence of chemical aging on physico-chemical properties of mineral dust particles: A case study of 2016 dust storms over Delhi
No full textThe physico-chemical properties of dust particles collected During Dust Storm (DDS) and After Dust Storm (ADS) events were studied using Scanning Electron Microscope coupled with Energy Dispersive Xray Spectroscopy (SEM-EDS), X-ray Fluorescence Spectroscopy (XRF) and X-ray Photoelectron Spectroscopy (XPS). Morphological and compositional change in dust particles were observed as they react with the anthropogenic pollutants present in the urban environment. The calcite rich particles were observed to transform into calcium chloride, calcium nitrate, and calcium sulfate on reacting with the chlorides, nitrates, and sulfates present in the urban atmosphere. The frequency distributions of Aspect Ratio (AR) for the DDS and ADS particles were observed to be bimodal (mode peaks at 1.2 and 1.5) and monomodal (mode peak at 1.1), respectively. The highly irregular shaped solid dust particles were observed to transform into nearly spherical semisolid particles in the urban environment. XPS analysis confirms the high concentration of oxides, nitrates, and chlorides at the surface of ADS samples which show the signatures of mineral dust particles aging. Species with a high value of imaginary part of refractive index (like Cr metal, Fe metal, Cr2O3, FeO, Fe2O3) were observed at the surface of dust particles. At 550 nm wavelength, the light-absorbing potential of the observed species along with black carbon (BC) was found to vary in the order; Cr metal > Fe metal > Cr2O3> FeO > BC > Fe2O3> FeOOH. The presence of the aforementioned species on the surface of ADS particles will tremendously affect the particle optical and radiative properties compared to that of DDS particles. The present work could reduce the uncertainty in the radiation budget estimations of mineral dust and assessment of their climatic impacts over Delhi
Investigation of charge transfer properties in MEHPVV and rGO-AA nanocomposites for Green organic photovoltaic application
No full textThe rapid ascension in conjugated polymer-based organic electronic device applications is of highest concern and explored with utmost interest. They own distinct properties such as efficient dissociation in exciton pairs and better charge transfer capabilities that lead to an enhanced separation of exciton at the donor: acceptor interface. Therefore, an appropriate selection of donor and acceptor species is required for the development of an efficient organic solar cell device. In this work, an organic nanocomposite-based system in which conductive polymer MEHPPV poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] acts as an electron donor and green route reduced graphene oxide (rGO) via L-Ascorbic Acid (L-AA) as an acceptor material has been materialised for the photovoltaic energy conversion. The validation of charge-transfer properties in rGO-AA blended with conducting MEHPPV has been investigated using photoluminescence quenching phenomena and UV visible spectroscopy techniques. However, the reduction of GO is confirmed using X-ray diffraction, Raman spectroscopy, and morphology via scanning electron microscopy. The current-voltage characteristics reveal that the charge transfer occurred and an efficiency of 0.084 % has been noticed which confirms the utilisation of rGO-AA as an acceptor material for the development of green optoelectronic devices
Mechanistic insights into defect generation and tuning of optical properties in Zn1-xFexAl2O4 (0.01 <= x <= 0.40) nanocrystals
No full textThe correlation of several defects and optical and magnetic properties with Fe content in Zn1-xFexAl2O4 (0.01 <= x <= 0.40) nanocrystals has been scrutinized through X-ray diffraction, O K-edge X-ray absorption near-edge structure, FT-IR, diffuse reflectance, photoluminescence and electron spin-resonance spectroscopies, and vibrating sample magnetometry. Increasing Fe content causes elongation in the octahedral units of the lattice, accompanied by distortion in the octahedral coordination. Fe introduces non-radiative centres in the forbidden gap, thereby tuning the band gap from 4.37 to 3.88 eV and eliminating emission in the visible region. Zn vacancies are found to tail off, while Fe-i(center dot center dot center dot), Al-Zn(center dot) and Fe-Al(x) antisite defects increase in concentration with increasing Fe content. Inhomogeneous broadening of spin-resonance signals infers strong spin-lattice interactions of Fe3+ ions at distorted octahedral and non-symmetric tetrahedral sites. A transition is observed from paramagnetism to superparamagnetism at higher Fe concentrations. A visual colour change from pearly white to orange-brown is observed in Zn1-xFexAl2O4 nanocrystals with increasing Fe content, revealing its potential candidature for pigments in the paint and dye industries
A Special Section on Functional Nanomaterials for Solar Cells
No full textThe process of bringing out a special section for Journal
of Nanoscience and Nanotechnology started with Dr. H. S.
Nalwa inviting to bring out a special section on topic
related to solar cells. During the course of discussion
we came upon the topic of “functional nanomaterials for
solar cells.” The purpose of this special section of Journal of Nanoscience and Nanotechnology is to summarize
the recent developments in this important research field.
Therefore, original research articles, short communications
and review articles were invited on all types of functional
nonomaterials associated with solar cells. Upon receiving
the invitation several authors were kind enough to accept
to contribute. Finally, the special section is being published with forty-two manuscripts, out of which four are
review articles. The topics are focused on nanoscience and
nanotechnology aspects of solar cells covering synthesis,
spectroscopic characterization, properties, and applications
of all types of nanomaterials in solar cells involving photodiodes, photodetectors, photoelectrochemical, etc. The
research topics include nanofabrication and processing,
manipulation, computational simulation, nanomachining,
structure analysis, applications in nanoelectronics, nanooptics and nanophotonics using all kinds of materials
which are parts of solar cell (absorber materials, buffer
layers, transparent conducting oxide, up-conversion, down
conversion materials, back and front contact, etc.)
Integrated graphene quantum dot decorated functionalized nanosheet biosensor for mycotoxin detection
Get PDFDecoration of graphene quantum dots (GQDs) on molybdenum disulfide (MoS2) nanosheets serves as an active electrode material which enhances the electrochemical performance of the analyte detection system. Herein, ionic surfactant cetyltrimethylammonium bromide (CTAB)-exfoliated MoS2 nanosheets decorated with GQD material are used to construct an electrochemical biosensor for aflatoxin B1 (AFB1) detection. An antibody of AFB1 (aAFB1) was immobilized on the electrophoretically deposited MoS2@GQDs film on the indium tin oxide (ITO)-coated glass surface using a crosslinker for the fabrication of the biosensor. The immunosensing study investigated by the electrochemical method revealed a signal response in the range of 0.1 to 3.0 ng/mL AFB1 concentration with a detection limit of 0.09 ng/mL. Also, electrochemical parameters such as diffusion coefficient and heterogeneous electron transfer (HET) were calculated and found to be 1.67 x 10(-5) cm(2)/s and 2 x 10(-5)cm/s, respectively. The effective conjugation of MoS2@GQDs that provides abundant exposed edge sites, large surface area, improved electrical conductivity, and electrocatalytic activity has led to an excellent biosensing performance with enhanced electrochemical parameters. Validation of the fabricated immunosensor was performed in a spiked maize sample, and a good percentage of recoveries within an acceptable range were obtained (80.2 to 98.3%)
Investigation of vacuum evaporated SnTe thin films for their structural, electrical and thermoelectric properties
Get PDFRemarkable enhancement in figure-of-merit (ZT) value of p-type Tin Telluride (SnTe) thin films is reported in the present investigations. Under high vacuum conditions, all thin films deposited on the glass substrate by using thermal evaporation technique. Thickness of the thin films were kept 55 and 33 nm. Morphological features and the elemental composition of the thin film were investigated using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) technique respectively. High-resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED) pattern was used to investigate the microstructure of these thin films. For the identification of crystalline features, phase, and nano-crystallites size in all the thin films, the X-ray diffraction (XRD) technique had played a dominant role. The analysis of the XRD data results in a single-phase cubic structure. Atomic force microscopy (AFM) analysis revealed the 2D and 3D view of variable size grains formed on the glass substrate. Four probes method was used to determine the electrical conductivity of these thin films. Electrical measurements revealed the semi-metallic nature of the SnTe thin films. The thermoelectric measurement analysis revealed that the ZT of the thin films was found to be increased as the thickness of the film enhanced. The maximum value of ZT similar to 1.0 was obtained at room temperature for the film of thickness 55 nm
LaScO3/SrTiO3: A conducting polar heterointerface of two 3d band insulating perovskites
Get PDFThis work reports a quasi-two-dimensional electron gas (q-2DEG) system at the interface of two wideband-gap insulators, (TiO2-terminated) SrTiO3 and LaScO3, with a minimum thickness of 4-unit cell (uc). The highly crystalline and abrupt heterointerface is confirmed with high-resolution electron microscopy. The mixed Ti4+ and Ti3+ valence states (for 4 uc of LaScO3) obtained from the x-ray photoelectron spectroscopy study suggest an intrinsic electronic reconstruction at the interface, leading to a metallic nature. This origin is well supported by density functional theory calculations that reveal an emergence of 3.3 states/eV/spin at the Fermi level for 4 uc in accordance with the polar catastrophe model. The study offers one more perovskite heterostructure, like LaAlO3/SrTiO3, for unraveling the q-2DEG phenomena toward a clear mechanism and futuristic applications