Browsing by Author "Prayas Chandra Patel"

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Advancing Cryogenic Cooling with Self-Modulated YbAgCu4 for Enhanced Thermoelectric Efficiency below Liquid-Nitrogen Temperatures
(American Chemical Society, 2023) Prayas Chandra Patel; Pankaj K. Mishra; Jyoti Kashyap
This report presents a comprehensive study of the thermoelectric performance of self-modulated YbAgCu4 for cryogenic cooling, T < 50 K. Implementing self-modulation-based nanostructuring by spark-plasma-sintering of powdered sintered and as-spun ribbons together, we obtained a high power factor of ∼2.3 × 10-2 W·m-1·K-2. The grain-boundary scattering in the prepared nanostructured samples significantly decreased the thermal conductivity as compared to the earlier reported values in polycrystalline YbAgCu4. In the present work, the peak thermoelectric figure-of-merit ZT of ∼0.32 at ∼43 K was achieved in the modulated sample. Such never before achieved high ZT at this temperature establishes the applicability of present methodology for cryogenic cooling below 77 K, which could further be extended to other heavy-Fermion materials to enhance their thermoelectric performances. © 2023 American Chemical Society.
Antiferromagnetic coupling in Co-doped ZnS
(Kluwer Academic Publishers, 2015) Prayas Chandra Patel; Surajit Ghosh; P.C. Srivastava
In this paper, we report room-temperature ferromagnetism in chemically synthesized Zn1−xCoxS (0 ≤ x ≤ 0.10) diluted magnetic semiconductor nanoparticles of ~3–5 nm. The incorporation of Co2+ ion for Zn2+ ions in ZnS lattice and the particle size were confirmed by XRD and TEM along with selected area electron diffraction analysis. UV–Vis measurement showed reduction in the bandgap energy with the increase in Co doping. Maximum magnetization was observed for samples with x = 0.04. From photoluminescence, spectra luminescence efficiency was found to get enhanced on Co doping. Magnetization behavior can be understood to be due to defect-induced ferromagnetism; however, for higher doping concentration, the antiferromagnetic coupling of Co–Co interaction in the close proximity results in the decrease of the overall magnetization of the samples. Moreover, magneto-electronic study also showed a maximum negative magneto-resistance of ~43 % for x = 0.04. © 2015, Springer Science+Business Media New York.
Bound magnetic polaron driven room-temperature ferromagnetism in Ni doped ZnS nanoparticles
(Elsevier Ltd, 2018) Prayas Chandra Patel; Surajit Ghosh; P.C. Srivastava
Magnetism in dilute magnetic semiconductors (DMSs) has been a controversial topic since its discovery. There are many models which predict the origin of room temperature ferromagnetism (RTFM) in TM doped wide band gap semiconductors. Here, we report RTFM in chemically synthesized cubic Zn1-xNixS (0 ≤ x ≤ 0.08) DMS nanoparticles of ∼3–5 nm size. Ferromagnetic behavior (at 300 K and 5 K) was found to increase with the increase in Ni doping concentration and was understood due to defect induced ferromagnetism. The low temperature magnetization measurement (ZFC-FC) shows that the nanoparticles are strongly coupled by magnetic interactions. Optical studies showed decrease in the energy bandgap along with the presence of sulfur and zinc vacancies and surface defects. Low temperature resistivity measurement depicted the semiconducting nature of the synthesized samples. With increase in doping concentration, an increase in the resistive behavior was observed which was explained in the realm of defects states created due to doping of the Ni ions. © 2018 Elsevier B.V.
Effect of impurity concentration on optical and magnetic properties in ZnS:Cu nanoparticles
(Elsevier B.V., 2017) Prayas Chandra Patel; Surajit Ghosh; P.C. Srivastava
To obtain enhanced room temperature ferromagnetism (RTFM) along with the increase in optical bandgap in the compound semiconductors has been an interesting topic. Here, we report RTFM along with increase in energy bandgap in chemically synthesized Zn1−xCuxS (0 ≤ x ≤ 0.04) DMS nanoparticles. Structural properties of the synthesized samples studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show the formation of cubic phase Cu doped ZnS nanoparticles of ~3–5 nm size. An intrinsic weak ferromagnetic behavior was observed in pure ZnS sample (at 300 K) which got increased in Cu doped samples and was understood due to defect induced ferromagnetism. UV–vis measurement showed increase in the energy bandgap with the increase in Cu doping. The PL study suggested the presence of sulfur and zinc vacancies and surface defects which were understood contributing to the intrinsic FM behavior. © 2017 Elsevier B.V.
Enhanced Photocatalytic Activity and Low Temperature Magnetic/Transport Study of Cu-Doped ZnS-Based Diluted Magnetic Semiconductor Nanoparticles
(Springer New York LLC, 2019) Prayas Chandra Patel; Surajit Ghosh; Pankaj Kumar Mishra; P.C. Srivastava
Diluted magnetic semiconductors (DMSs), having interesting magnetic/transport properties, are currently being explored in photocatalytic application as well. This report presents photocatalytic and low temperature magnetic/transport study of chemically synthesized 3-5 nm sized cubic Zn1-xCuxS (0 ≤ x ≤ 0.04) DMS nanoparticles. Both studies have their own importance, former relates to dye degradation, while later attempts to understand origin of magnetic behavior in DMSs (which is still debatable). As a photocatalyst, Cu doped ZnS NPs showed enhanced degradation-efficiency for methylene blue dye. Magnetization study showed enhanced magnetic moment in Cu doped samples, which in the low temperature regime got further enhanced and was understood due to defect induced ferromagnetism. Low temperature transport study showed the decrease in resistivity of the Cu doped samples and was understood in terms of defects states created due to doping of the Cu ions and governed by conduction mechanism, namely thermal activation and variable range hopping. © 2019, The Minerals, Metals & Materials Society.
Fe doping in ZnS for realizing nanocrystalline-diluted magnetic semiconductor phase
(Kluwer Academic Publishers, 2014) Prayas Chandra Patel; P.C. Srivastava
Zn1-x Fe x S (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.12, and 0.15) samples have been synthesized by the chemical co-precipitation method, using ZnCl2 and Na2S as starting materials, FeCl3 as a dopant and Ethylenediaminetetraacetic acid (EDTA) as capping agent. Investigations of the structural, optical, and magnetic properties of the prepared samples have been carried out. The results of X-ray diffraction (XRD), selected area electron diffraction of TEM images, Fourier transform infrared spectroscopy have shown that Fe ions are incorporated into the lattice of ZnS crystallites as substitutional impurity at Zn sites in the structure without disturbing the original ZnS wurtzite structure. The average crystallite size from the XRD data and transmission electron microscopy has been found to be in the range of 4-10 nm. Magnetization behavior (i.e., M-H Characteristics) shows the evolution of ferromagnetic behavior with Fe incorporation. It has been found that there is an optimum iron ion concentration for observing the maximum magnetization. The optimum iron ion concentration has been found to be, x = 0.08 in the synthesized samples of Zn1-x Fe x S. The observed magnetization behavior has been understood as ferromagnetic behavior of Fe ions. The decrease of ferromagnetism for the higher Fe ion concentration has been discussed as a result of Fe-Fe interaction in close proximity to result antiferromagnetism for decreasing the magnetization. © 2014 Springer Science+Business Media New York.
Fe-As Intermetallic Alloys: A Way Out for Sodium-Ion Batteries
(American Chemical Society, 2023) Prayas Chandra Patel; Surabhi Awasthi; Pankaj Kumar Mishra; Priyanka Lakharwal; Jyoti Kashyap
Intermetallic alloy anodes with high theoretical sodiation capacities are highly sought for next-generation sodium-ion batteries (SIBs). Here, we demonstrate the fabrication of a high-performance intermetallic Fe-As alloy anode for high capacity sodium-ion batteries (SIBs) via a high-throughput and industrially viable melt-spinning process. This earth-abundant low-cost alloy anode exhibits highly enhanced cycling stability, retaining 96% of its 965 mAh·g-1 sodiation capacity after 400 cycles at 50 mA g-1 specific current for SIBs. The exceptional electrochemical performance of the prepared alloy anode is attributed to the crystalline features of the melt-spun fibers, which also enable a remarkable rate performance with ∼668 mAh g-1 sodiation capacity at 5 A g-1. We further demonstrated the application of the prepared alloy anode in a sodium-ion full-cell configuration, where it delivered a sodiation capacity of over 770 mAh g-1 (based on anode) at 50 mA g-1, achieving more than 97% Coulombic efficiency even after 200 cycles. Our results suggest that melt-spun alloy anodes hold great potential for realizing fully functional SIBs. © 2023 American Chemical Society.
Fine-Grained Bi-Sb Ribbons with Modulation-Doped FeSb Nanoparticles for High-Temperature Cryogenic Applications
(American Chemical Society, 2022) Prayas Chandra Patel; Pankaj K. Mishra; Hem Chandra Kandpal
With about two-thirds of global energy being lost as waste heat, improvement in the mutual conversion of heat and electrical energy is a "must" with the continued growth in demand. The present report investigates the dramatic improvement of thermoelectric performance (ZT) in a well-studied system by utilizing the intrinsic magnetic field generated from within the material. The concept was to utilize the intrinsic magnetic field induced by the randomly dispersed multisized magnetic (FeSb) nanoparticles spread throughout the host TE material (Bi-Sb). It thus modified the transport properties, i.e., electrical/thermal conductivity and Seebeck coefficient, so as to give a record jump of ∼155% in the peak ZT of the referenced material and increased it to 0.79 from 0.32. Interestingly, the application of an external magnetic field further increased the ZT by ∼57% (i.e., from 0.79 to 1.26), thus giving an overall improvement of ∼300% (from 0.32 to 1.26) as compared to the referenced material. What is particularly exciting is that this simple idea of modulation doping of ferromagnetic nanoparticles can also be extended to other important thermoelectric materials. © 2022 American Chemical Society. All rights reserved.
Hysteresis in magnetoresistance and formation of spin glass like structure in PVA capped Fe3O4
(Springer New York LLC, 2017) Surajit Ghosh; Prayas Chandra Patel; P.C. Srivastava
Here, we report the temperature dependent hysteresis in the magneto transport in PVA capped Fe3O4 nanoparticles. The synthesis of the nanoparticles of size 10–15 nm were carried out via co-precipitation method followed by heat treatment at different temperatures. Structural studies confirm the formation of polycrystalline Fd 3 ¯ m phase of Fe3O4 when the samples were sintered up to 600 °C. FTIR studies show that PVA and magnetic grains were attached through hydrogen bonding between hydroxyl group of PVA and protonated surface of the oxide. Spin glass type transition was observed in the ZFC–FC plots at 125 K which is also the Verwey transition temperature TV as measured from the transport studies. A hysteresis in the MR plot was found which was explained in the realm of tunnel transport through ferromagnetic grain and antiferromagnetic surface of the ferrite particles. Tunnelling through the dielectric spacer layer of PVA has an overall impact to increase the resistance of the samples. The temperature dependence of the hysteresis gives a major hint to the origin of the spin glass type behaviour of the samples. © 2017, Springer Science+Business Media, LLC.
Low temperature magnetic study of α-NiS nanoparticles synthesized via hydrothermal technique
(Elsevier Ltd, 2021) Prayas Chandra Patel; Pankaj Kumar Mishra; Hem C. Kandpal
Synthesis of material with nano-order anisotropy has always been a tricky task for the researchers, since there has to be some property-based inhomogeneity present within the homogeneous material. In this report, we discuss the emergence of Exchange Bias (EB), which is itself a case of magnetic property based anisotropy. Here, a thorough low temperature magnetic study of nickel sulfide (NiS) nanoparticles synthesized via solution based hydrothermal technique was performed. To introduce nano-order inhomogeneity we played with different feeding flow rate of the starting materials. The synthesized samples were of highly crystalline mixed phase nature with α-NiS as a dominant phase. Variation in energy bandgap as a function of feeding rate suggests the possibility of the formation different-sized seed cluster. For sample with maximum α-NiS content, presence of strong magnetic coupling at T
Structural and Magnetic Studies of Thermally Treated NiFe2O4 Nanoparticles
(Springer Boston, 2017) Surajit Ghosh; Prayas Chandra Patel; Debraj Gangopadhyay; Poornima Sharma; Ranjan K. Singh; P.C. Srivastava
The heat treatment of nanoparticles can have a direct effect on their particle sizes, which, in turn, can influence many of their structural and magnetic properties. Here, we report the effect of sintering temperature on the chemically synthesized high-quality NiFe2O4 nanoparticles. The structural studies show the formation of pure NiFe2O4 nanoparticles with the space group Fd3 ¯ m. The inverse spinel structure was also confirmed from the lattice vibrations analyzed from Raman and Fourier transform infrared spectroscopy (FTIR) spectra. The presence of strong exchange interactions was detected from the temperature-dependent magnetization study. Moreover, at higher sintering temperatures, the grain growth due to fusion of several smaller particles by coalescing their surfaces enhances the crystallinity and its magnetocrystalline anisotropy. Coercivity and saturation magnetization were found to depend significantly on the sintering temperature, which was understood in the realm of the formation of single-domain-like structure and change in magnetocrystalline anisotropy at higher sintering temperatures. © 2017, The Minerals, Metals & Materials Society and ASM International.
Structural, magnetic and optical properties of ZnO nanostructures converted from ZnS nanoparticles
(Elsevier Ltd, 2016) Prayas Chandra Patel; Surajit Ghosh; P.C. Srivastava
The present work concentrates on the synthesis of cubic ZnS and hexagonal ZnO semiconducting nanoparticle from same precursor via co-precipitation method. The phase conversion of ZnS to highly crystalline hexagonal ZnO was done by heat treatment. From the analysis of influence of calcination temperature on the structural, optical and vibrational properties of the samples, an optimum temperature was found for the total conversion of ZnS nanoparticles to ZnO. Role of quantum confinement due to finite size is evident from the blue shift of the fundamental absorption in UV-vis spectra only in the ZnS nanoparticles. The semiconducting nature of the prepared samples is confirmed from the UV-vis, PL study and transport study. From the magnetic and transport studies, pure ZnO phase was found to be more prone to magnetic field. © 2016 Elsevier Ltd. All rights reserved.
Study of MAX phase based Schottky interfacial structure: the case of electron-beam deposited epitaxial Cr2AlC film on p–Si (100)
(Springer, 2023) Prayas Chandra Patel; Pankaj Kumar Mishra; Hem C. Kandpal
In recent times, due to their highly stable and radiation tolerant nature, interest toward feasibility of developing MAX phase-based applications has suddenly surged. In this context, we for the first time report a comprehensive spin-dependent transport study of Cr2AlC@p–Si-based thin film interfacial structure. Phase purity of the fabricated epitaxial Cr2AlC thin film grown by electron-beam deposition was confirmed from structural, vibrational and elemental analysis. Transport studies showed n-type metallic nature of the deposited Cr2AlC films. Low-temperature transport/magnetic measurements across the interface have shown spin-dependent Schottky behavior. Our results demonstrate the potential of Cr2AlC@p–Si as a novel Schottky interfacial structure for the development of more complex device applications. Graphical abstract: [Figure not available: see fulltext.] © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Synthesis of wurtzite ZnS nanocrystals at low temperature
(2013) Prayas Chandra Patel; Neelabh Srivastava; P.C. Srivastava
Nanocrystallites of wurtzite hexagonal ZnS have been successfully synthesized without using any capping agent by simple chemical precipitation method at a low calcination temperature of 150 C. It has been found that the size of the synthesized ZnS nanocrystallites decreases as Zn2+:S 2- ratio is decreased. The synthesized nanoparticles have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis absorption spectroscopy and M-H characteristics. The XRD patterns have confirmed that the prepared ZnS nanoparticles are of wurtzite hexagonal phase. XRD, SEM and TEM studies have shown the decrease in the particle size with the increase in S2- source. TEM images have clearly shown that size distribution of the particles lie in the range of 5-30 nm. The optical absorption bandgap of the synthesized nanocrystals has been found to be in the range of 3.69-3.74 eV. Magnetization study has shown the 'diamagnetic' behavior of synthesized ZnS nanocrystallites with a weak ferromagnetic behavior in the low field regime. The observed weak ferromagnetism has been understood due to the presence of defects in the synthesized ZnS nanoparticles. © 2013 Springer Science+Business Media New York.
Unusual Ferromagnetic to Paramagnetic Change and Bandgap Shift in ZnS:Cr Nanoparticles
(Springer New York LLC, 2019) Prayas Chandra Patel; Surajit Ghosh; P.C. Srivastava
We report the chemical synthesis of Cr-doped ZnS nanocrystallites without using any capping ligand/surfactant. An unusual increase in bandgap observed for Cr-doped samples was understood in terms of the Burstein–Moss effect. Additionally, 4A2(F) → 4T1(F) and 4A2(F) → 4T2(F) transitions in the absorption spectra confirmed the substitution of Cr3+ ions at the octahedrally coordinated interstitial sites. Photoluminescence study showed a large amount of Zn vacancies owing to the incorporation of Cr3+ ions which intensified the self-activated blue–green luminescence. Room-temperature magnetization showed FM ordering up to the 2% Cr doping, which gradually transformed into paramagnetic behavior at higher values and became more enhanced in the low-temperature range. Thus, in the present synthesis method, the FM order could only be observed up to the 2% Cr doping concentration. Also, the activation energy was observed to increase with the increase of Cr doping concentration. © 2019, The Minerals, Metals & Materials Society.